July 30, 2007

Frictionless Compressors

Are they right for you?

Compressors that run on frictionless bearings are an enticing prospect. Dan Foss Turbocor, Inc. is now marketing a line of compressors that use magnetic bearings to provide essentially frictionless operation. These compressors have been on the market for about three years, and now McQuay International is incorporating the compressors into their new line of frictionless chillers.

Using innovative technology that levitates the compressor shaft in a magnetic field, the compressors operate without metal-to-metal contact, making them more efficient, and eliminating the need for an oil management system. Turbocor has recently received three prestigious awards for this design: the ASHRAE/AHR Expo "Energy Innovation" Award in 2003, the Natural Resources Canada's Energy Efficiency Award in 2003, and the U.S. Environmental Protection Agency’s Climate Protection Award in 2004.

How are they different?
Here are some of the features, benefits, and concerns to help you decide whether frictionless compressors (or McQuay’s frictionless chillers) are right for you. Each feature is discussed in more detail below.

· Magnetic bearings.
· Oil-free design.
· Low noise Level
· VFD control.
· Soft start.
· Smaller and lighter than conventional compressors.
· Uses a centrifugal compressor.

Magnetic bearings
A digitally controlled magnetic bearing system, consisting of both permanent magnets and electromagnets, replaces conventional lubricated bearings. The only rotating part—the compressor shaft—is levitated and held in place by magnetic bearings, eliminating metal-to-metal contact, essentially eliminating friction.

Four positioning signals, sampling six million times per minute, hold the levitated position to within 0.00005” of center. The advantages of this technology include:
  • No friction. This can improve energy efficiency by 2-4%.
  • No metal-to-metal contact, therefore less wear on moving parts. Turbocor claims that maintenance costs are about half what they are for conventional technology.
  • The frictionless bearings, in conjunction with variable frequency drive (VFD) control, allow the shaft to spin at high speeds (up to 48,000 RPM) and give good speed control.
  • Very little vibration. Because of no physical contact, vibrations are small and tend to be self-dampened.

The magnetic bearing system, however, is more expensive and it takes some energy to operate the system. The levitation system on current models uses approximately 180 watts, or about 0.5% of the operating energy. Contrast this to 2-4% for conventional bearings, along with a lubrication system that (according to Turbocor) can use up to 10,000 watts.

Oil-free design

The biggest benefit to eliminating oil from the system is that it eliminates the need for a lubrication system, which can include oil pumps, sumps, oil separators, heaters, coolers, etc. In comparing the costs of two proposed systems, it important to consider lubrication in estimating both the capital and operating costs. The other disadvantage of having oil in the system is that it can reduce the effectiveness of heat transfer in the coil. The effect of this, however, is small. While the Turbocor website suggests that heat transfer effectiveness can be reduced by 15% or more by the presence of oil, this will most likely translate into a somewhat smaller effect on overall system efficiency.

Low noise level

The Turbocor compressors, by all reports, make significantly less noise than the comparable screw compressors. What noise there is tends to be high frequency, which is relatively easy to attenuate.

VFD control

The big potential savings of this system comes from the integrated variable frequency drive. This provides good speed control, allowing the system to run up to 48,000 RPM and (because there is no friction in the motor) it can also operate efficiently at low loads.

In addition, the compressor has automatically controlled inlet guide vanes that unload further in low-load conditions. These features give the system an excellent integrated part-load value (IPLV) rating. Many chillers in HVAC applications are running at part load a vast majority of the time, making them an excellent application for the frictionless system.

Turbocor claims that they have achieved an IPLV rating as low as 0.375 kW/Ton, compared to 0.63 kW/Ton for the Turbocor at full load, and 0.5 kW/Ton being considered a very good rating. Herein lies the key to a successful application of Turbocor. If the chiller will be operated at part load a good proportion of the time, a frictionless chiller is worth considering.

Soft start

An added benefit of having the integrated VFD is that the motor has a built-in soft start. Turbocor uses a unique method of soft start that ramps the motor up gradually, making inrush current effectively the full load current. On Turbocor’s website, they list the inrush current as 2 amps, or 5 amps in some places, meaning, presumably, that the ramping up process starts with this very low current. It is not clear how this information is useful, since the information about inrush current is generally used for sizing circuit breakers. The breaker would simply have to be sized for the full load amperage.

Small and Lighter

Using permanent magnets in the motor, rather than electrical windings as in an induction motor, reduces the size and weight significantly. In addition, by running the shaft at high speeds, they are able to use a smaller, lighter, shaft. According to the manufacturer, the Turbocor compressors, at 265 lbs., are one-fifth of the weight and half the size of an equivalent conventional compressor.

Uses a centrifugal compressor

Centrifugal compressors tend to be more efficient than screw or scroll compressors, and take advantage of speed control more effectively, but they are usually only available in larger sizes. By using the smaller shaft, they are able to take advantage of the centrifugal compressor technology in a smaller size than is normally available.


Is it a Right Choice - Baby?
That depends. The design of these compressors is clearly innovative, elegant, and efficient, and all indications are that it is a quality product. The idea of using magnetic bearings is provocative, but it turns out that this feature in itself is rarely enough to justify considering the 50-70% price premium you are likely to pay for a frictionless compressor. However, with associated benefits, it may be well worth considering.

Remember to take into consideration not having to include an oil management system, and perhaps easier and quicker installation. Certainly in an application where the chiller runs at part load much of the time, such as in many HVAC applications, the efficiency may be much better. In that case, the IPLV rating will be a better indication of the relative performance than the full-load rating, but it will probably be worthwhile to have an engineer do a full analysis of the relative costs based on your particular application. The more your chiller will be running at part load, the more attractive this product will be. Reduced maintenance costs may tip the scales in favor of going frictionless.


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New Section on This Blog

Today I have just added one section for good Chemical Engineering Jobs for everyone.

This is available at the top of the title of my Blog in blue color. You can see two tabs - Home & CHE Jobs. I have added it to provide all info to my visitors at one place.
I am busy in this week preparing for a national seminar on "Alkoxyaltion Technology - Reactor Development". I will post it later after coming back on 12 July'2007.
Sooner I am going to add my detailed profile to my blog. It may be today also or may be after 12th July.



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July 26, 2007

Useful Tips on Use of ASD/VFD for pumps

Potential Applications

ASDs are ideally suited for variable-torque loads from centrifugal pumps, fans, and blowers when the system load requirements (head, flow, or both) vary with time. Conditions that tend to make ASDs cost-effective include the following:
  1. High horsepower (greater than 15 to 30 hp)—the higher the pump horsepower, the more cost-effective the ASD application.

  2. Load type—Centrifugal loads with variable-torque requirements (such as centrifugal pumps or fans) have the greatest potential for energy savings. ASDs can be cost-effective on positive displacement pumps, but the savings will generally not be as great as with centrifugal loads.

  3. Operating hours—In general, ASDs are cost-effective only on pumps that operate for at least 2,000 hours per year at average utility rates.

  4. High utility rates—higher utility energy charges provide a more rapid payback on an investment in an ASD.

  5. Availability of efficiency incentives—where they are available, electric utility incentives for reducing energy use or installing energy-saving technologies will reduce payback periods.

  6. Low static head—ASDs are ideal for circulating pumping systems in which the system curve is defined by dynamic or friction head losses. They can also be effective in static-dominated systems—but only when the pump is carefully selected. A thorough understanding of pump and system interactions is critical for such applications.


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Learnings from leakage in Phosphoric acid plant

System Background
In the concentrator section of phosphoric acid plant, weak phosphoric acid is concentrated by evaporation in graphite made evaporator. This is normally operated under vacuum & ~88°C temperature due to highly corrosive nature of phosphoric acid (PA). Over a period of time, the tubes of this exchanger require cleaning for removal of deposits & fouling material. This is a normal practice in both plants i.e. PAP-I & PAP-II.

The weak acid is filled in the tube side of this exchanger at atmospheric condition & after closing the system & pulling the vacuum; steam is injected for raising the temperature. This steam is fed into the shell side of this evaporator @ 3.5 to 4 kg/cm2g. The condensate formed is collected in a small vessel of ~2 m3. This condensate is pumped to the main condensate storage tank CST-1 in main CPP plant.

The vent from this small condensate tank of PAP plant goes to barometric condenser for sealing, which was isolated later on. From the top of the condensate tank, one more line of ½” is provided which acts as an overflow drain. The discharge system is having one conductivity meter, which is used to monitor the quality of condensate being sent to CST-1. In case, conductivity of discharge condensate increases, the pump discharge is manually diverted to the local drain in cooling tower system to avoid any contamination in CPP.

Incidence Sequence
    >
  1. The said evaporator was under hydro jet cleaning on 26th Oct’2004 in PAP-II.

  2. AAfterwards, it was taken under filling with weak PA at @ 2004 hrs.

  3. The PA acid filling rate was 75 m3/hr @2034 hrs.

  4. @ 2034 hrs, the level in condensate tank in PAP-II was 3.9%.

  5. The conductivity meter was showing a normal reading of 16 -cm/s.

  6. @ 2040 hrs, the condensate tank high-level alarm appeared in control room.

  7. Till the time, steam was not going to the evaporator.

  8. @ 2150 hrs condensate pump was started to transfer the liquid from condensate tank to CPP, but it tripped.

  9. The conductivity meter was showing a reading of 1.5 -cm/s.

  10. @ 2150 hrs it was found that inlet drain of this pump was in choked condition & pump was tripping on overload, which Electrical Deptt did inform.

  11. @ 2250 hrs the drain of pump was dechoked manually & it was found by the operator that PA acid was coming out form this drain.

  12. Therefore, acid filling in the evaporator was stopped @ 2250 hrs.

  13. @ 2300 hrs the draining of evaporator was started.

  14. Meanwhile it was found in the smelter WHB area & in AFBC boiler area that the gaskets on joints were leaking out after cracks & PA acid with water was coming out from them.

Comments after Analysis
After discussion with all concerned staff of PAP plant, Technical improvement Cell (TIC), CPP, Water treatment section & other executives, CTC came to following conclusive points.

  1. The first apparent incidence was the condensate tank high-level alarm @2040 hrs. When there was no steam inlet to the system, this condensate tank high-level alarm should not appear. It indicates tube side leakage in the evaporator.

  2. The indication & behavior of conductivity meter was erratic. If actual condensate conductivity goes high beyond its full range value of 16 it resets itself & shows a reading of say 19 as 3 -cm/s. This kind of behavior of any instrument is very uncommon in the industries. In this case, it should report stack or data overflow.

  3. Because of resetting of the conductivity meter reading the operator is not aware of current range of actual value whether it is over critical limit or under critical limit at any point of time. So this instrument becomes irrelevant for the operational decision. In fact, it can be dangerously misleading.

  4. Because of new value of 1.5 -cm/s, operator cannot immediately judge/identify the problem of high conductivity or any leakage in the system.

  5. The liquid filling rate of 75 m3/hr / normal steam consumption rate of 35 to 40 TPH suggest that the capacity of 2 m3 of the existing condensate tank in PAP plant is not designed to hold acidic water .

  6. It should have sizeable top / overflow line, which can take care of any leakage in the system considering its corrosive nature. The size of drain line is not sufficient to take up even 10 m3/hr influx of liquid. So the leakage influx could not be drained out.

  7. There was no second measure for safety in this critical system. Considering its highly corrosive nature it should have at least two simultaneous systems to avoid any criticality due to system & operational failures.

Suggestions


  1. Material of construction (MOC) of the existing evaporator in PAP-II is from M/s. Graphite India whereas; PAP-I evaporator is from M/s. Le-Carbon. Based on our past experience, we suggest that the quality of Le-Carbon make graphite is superior to Graphite India Make. Therefore, Unit should replace the MOC of existing evaporator with Le-Carbon make in the next available opportunity.

  2. Unit should install 2 highly reliable conductivity meters (it should have display range up to 100 -cm/s), also if conductivity exceeds this limit, indication should stay at maximum value.

  3. One of this conductivity meters should be installed in incoming line of condensate, which is transferring the steam condensate from evaporator to the new hold up tank, with a provision of three-way valve. In case, conductivity goes beyond normal value (say 16), it will divert the condensate feed from holdup tank to drain pit.


  4. The holdup tank should be provided with a LIC & level control valve in the discharge of pump. The pump motor should also have startup interlock with high conductivity.

  5. In the transfer line from holdup tank to CST in CPP, there should be another meter with three-way valve. In case, conductivity goes beyond normal value (say 16), it will divert the condensate from pump discharge to drain pit.

  6. Both of the proposed three-way valves will operate in one direction either in draining mode or in-line mode based on the higher reading out of two conductivity meters.

  7. Overflow drain line should be 2” in size.

  8. It is also recommended to train the staff on HAZOP aspects after detailed HAZOP study of PAP plants.


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July 25, 2007

Corn: Another Chemical Use - Polypropylene Glycol

An industrial chemical found in antifreeze, de-icing fluids, and liquid detergents could soon stand alongside animal feeds, sweeteners and cooking oil as a commercial product made from corn.

Randy Cortright and James Dumesic, chemical engineers at the University of Wisconsin-Madison, have invented a catalytic process for converting the corn-derived compound, lactic acid, into the chemical polypropylene glycol. More than 450 MT of polypropylene glycol are used in the United States annually.

Unlike current processes for manufacturing polypropylene glycol, which make use of petroleum-based starting materials, this advance taps into a low cost, renewable resource available in surplus right now. The U.S. Department of Agriculture estimates that over a billion bushels of corn went unused last year.

"This technology provides a sustainable method of producing important chemicals," Cortright says. It also promises to reduce reliance on imported oil and open new markets for U.S.-grown corn.

A chain of processes links corn to polypropylene glycol. It begins with fermentation of the corn-derived sugar glucose into lactic acid, followed by separation and purification of the acid. Cortright and Dumesic's method completes the critical last step by using a copper catalyst in the presence of hydrogen gas to chemically transform lactic acid into polypropylene glycol.
The approach is more cost-efficient than past methods, Cortright says. "We're using a relatively inexpensive metal, running the reaction at lower [hydrogen] pressure and we get 100 percent conversion," of the lactic acid, with fewer unwanted byproducts like alcohols.

Cortright and Dumesic's research builds upon the work of Homer Adkins, a UW-Madison chemistry professor from 1919-49. At a time when most chemicals were produced from agricultural products rather than oil, Cortright says, Adkins was the first to use copper catalysts to turn lactic acid into propylene glycol. "It feels like we've come full circle," Cortright says, "We enhanced the technology, but the basic ideas were known 70 years ago."

Source: University Of Wisconsin, Madison.

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Ways to Save Energy in Pumps

Here is my experience based on energy audits of pumping systems in various chemical, metal, textile & petrochemical units.
  • Design systems with lower capacity and total head.

  1. Do not assume these requirements are fixed.

  2. Calculate flow requirement based on actual mathematical nos without margins in each stage & then add 10-20% straightforward as Normal capacity of the pump. For example if process side heat load in an exchanger is based on normal flow of say 100 M3/hr then do not consider cooling water requirement for peak condition of 120 or say 140 M3/hr. Just calculate it based on normal flow of 100 M3/hr at this stage.

  3. Total head requirements can be reduced by: lowering process static gage, pressure, minimizing elevation rise from suction tank to discharge tank, reducing static elevation change by use of siphons, lowering spray nozzle velocities, lowering friction losses through use of larger pipes and low-loss fittings, and eliminating throttle valves.

  4. After calculating total requirement of Flow & Head this way, simply add 10-20% in both parameters as design margin based on your judgement about process variation. This should be your normal capacity. You still have higher margins becasue rated condition are further higher than these values.

  5. Also keep in mind that worst conditions dont come all simultaneously. You can still meet few peak demands.

  6. Dont worry about undersizing of your pump. You can add later & this approach is beneficial in overall longer run as you can switch your additional capacity ON & OFF.

  7. This can give you a saving of ~10-20% in your pumping system. A thorough review is must.
  • Emphasize on Efficiency first
  1. Despite the tendency to emphasize initial cost, you will save cost in the long run by selecting the most efficient pump type and size at the onset.

  2. The choice of a pump depends on the service needed from the pump. Considerations are flow and head requirements, inlet pressure or net positive suction head available, and the type of liquid to be pumped.

  3. Maximum attainable efficiency of a centrifugal pump is influenced by the designer's selection of pump rotating speed as it relates to "specific speed." Purchasers need to be aware of this, as well as the decision criteria for determining the type of pump to use.

  4. Consider LCC (Life Cycle Costing) option instead of initial cost only. Click here to learn more about LCC Analysis.

  5. Remember ENERGY is the most expensive "commodity" today.

  6. People generally loose ~80% more money due to non LCC approach over a period of its service life.

  • Divided Use

  1. Design or select no of pumps based on different possible scenarios & always follow the operation philosophy of bulk & makeup supply for any system.

  2. This approach saves at least 10-15% over conventional selection of equal size pumps.

  3. This helps in putting the smaller pump on auto mode with header pressure switch so that excess pump capacity can be turned on/off.

  4. Two pumps can be operated in parallel during peak demand periods, with one pump operating by itself during lower demand periods. Energy savings result from running each pump at a more efficient operating point and avoiding the need to throttle a large pump during low demand.

  5. Analternative is to use one variable-speed pump and one constant-speed pump. Use or selection depends on the process behaviour e.g. how fast the demand is changing? How many time it is changing? Is my process critical? etc.

  • Avoid end of curve operation
  1. Generally in case of cooling water pumps head & flow both are selected with plenty of margins, comfortable to the cushion needed by selection manager. This results in near end curve operation without throttling. This is worst operation of pumps in almost every situation. Avoid it.


  • Use pumps as drives
  1. Use them as drivers / turbines to recover pressure energy that would otherwise be wasted.

  2. Practically all centrifugal pumps will perform as turbines when operated in reverse.

  3. A hydraulic power recovery turbine can recover pressure energy when used to drive a generator, or assist the driver of a pump or a compressor.



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July 24, 2007

Life Cycle Cost (LCC) Analysis

Life-cycle cost analysis (LCCA) is a method for assessing the total cost of facility ownership. It takes into account all costs of acquiring, owning, and disposing of a project. LCCA is especially useful when project alternatives that fulfill the same performance requirements, but differ with respect to initial costs and operating costs, have to be compared in order to select the one that maximizes net savings.

For example, LCCA will help determine whether the incorporation of a good HVAC or glazing system, which may increase initial cost but result in dramatically reduced operating and maintenance costs, is cost-effective or not.

LCCA is not useful for budget allocation.

Lowest life-cycle cost (LCC) is the most straightforward and easy-to-interpret measure of economic evaluation. Some other commonly used measures are Net Savings (or Net Benefits), Savings-to-Investment Ratio (or Savings Benefit-to-Cost Ratio), Internal Rate of Return, and Payback Period. They are consistent with the Lowest LCC measure of evaluation if they use the same parameters and length of study period. The approach to making cost-effective choices for projects can be quite similar.

A. Life-Cycle Cost Analysis (LCCA) Method

The purpose of an LCCA is to estimate the overall costs of project alternatives and to select the design that ensures the facility will provide the lowest overall cost of ownership consistent with its quality and function. The LCCA should be performed early in the design process while there is still a chance to refine the design to ensure a reduction in life-cycle costs (LCC).

The first and most challenging task of an LCCA, or any economic evaluation method, is to determine the economic effects of alternative designs of project and to quantify these effects and express them in money terms.


B. Costs


There are numerous costs associated with acquiring, operating, maintaining, and disposing of a project. Related costs usually fall into the following categories:

  • Initial Costs—Purchase, Acquisition, Construction Costs

  • Fuel Costs

  • Operation, Maintenance, and Repair Costs

  • Replacement Costs

  • Residual Values—Resale or Salvage Values or Disposal Costs

  • Finance Charges—Loan Interest Payments

  • Non-Monetary Benefits or Costs

Only those costs within each category that are relevant to the decision and significant in amount are needed to make a valid investment decision. Costs are relevant when they are different for one alternative compared with another; costs are significant when they are large enough to make a credible difference in the LCC of a project alternative. All costs are entered as base-year amounts in today's money; the LCCA method escalates all amounts to their future year of occurrence and discounts them back to the base date to convert them to present values.

Initial costs
Initial costs may include capital investment costs for land acquisition, construction, or renovation and for the equipment needed to operate a facility.

Land acquisition costs need to be included in the initial cost estimate if they differ among design alternatives. This would be the case, for example, when comparing the cost of renovating an existing facility with new construction on purchased land.

Construction costs

Detailed estimates of construction costs are not necessary for preliminary economic analyses of alternative designs or systems. Such estimates are usually not available until the design is quite advanced and the opportunity for cost-reducing design changes has been missed. LCCA can be repeated throughout the design process if more detailed cost information becomes available. Initially, construction costs are estimated by reference to historical data from similar facilities.

Energy and Water Costs

Operational expenses for energy, water, and other utilities are based on consumption, current rates, and price projections. Energy costs are often difficult to predict accurately in the design phase of a project. Assumptions must be made about use profiles, Efficiency variations, and schedules, all of which impact energy consumption. At the initial design stage, data on the amount of energy consumption can come from engineering analysis.

Energy prices

Quotes of current energy prices from local suppliers should take into account the rate type, the rate structure, summer and winter differentials, block rates, and demand charges to obtain an estimate as close as possible to the actual energy cost.

Energy price projections

Energy prices are assumed to increase or decrease at a rate different from general price inflation. This differential energy price escalation needs to be taken into account when estimating future energy costs. Energy price projections can be obtained either from the supplier or from energy price escalation rates published annually on April 1 by DOE in Discount Factors for Life-Cycle Cost Analysis, Annual Supplement to NIST Handbook 135.

Water Costs

Water costs should be handled much like energy costs. There are usually two types of water costs: water usage costs and water disposal costs.

Operation, Maintenance, and Repair Costs

Non-fuel operating costs, and maintenance and repair (OM&R) costs are often more difficult to estimate than other expenditures. Operating schedules and standards of maintenance vary from project to project and equipment to equipment; there is great variation in these costs even for projects / equipments of the same type and age. It is therefore especially important to use engineering judgment when estimating these costs.

Replacement Costs

The number and timing of capital replacements of equipments depend on the estimated life of the system and the length of the study period. Use the same sources that provide cost estimates for initial investments to obtain estimates of replacement costs and expected useful lives. A good starting point for estimating future replacement costs is to use their cost as of the base date. The LCCA method will escalate base-year amounts to their future time of occurrence.

Residual Values

The residual value of a system (or component) is its remaining value at the end of the study period, or at the time it is replaced during the study period. Residual values can be based on value in place, resale value, salvage value, or scrap value, net of any selling, conversion, or disposal costs. As a rule of thumb, the residual value of a system with remaining useful life in place can be calculated by linearly prorating its initial costs. For example, for a system with an expected useful life of 15 years, which was installed 5 years before the end of the study period, the residual value would be approximately 2/3 (=(15-10)/15) of its initial cost.


Other Costs

Finance charges and taxes: For small projects, finance charges are usually not relevant. Finance charges and other payments apply, however, if a project is financed through any outside agency. The finance charges are usually included in the contract payments negotiated with the Energy Service Company (ESCO) or the utility.

Non-monetary benefits or costs

Non-monetary benefits or costs are project-related effects for which there is no objective way of assigning a dollar value. Examples of non-monetary effects may be the benefit derived from a particularly quiet HVAC system or from an expected, but hard-to-quantify productivity gain due to improved lighting. By their nature, these effects are external to the LCCA, but if they are significant they should be considered in the final investment decision and included in the project documentation.

To formalize the inclusion of non-monetary costs or benefits in your decision making, you can use the analytical hierarchy process (AHP), which is one of a set of multi-attribute decision analysis (MADA) methods that consider non-monetary attributes (qualitative and quantitative) in addition to common economic evaluation measures when evaluating project alternatives.

C. Life-Cycle Cost Calculation

After identifying all costs by year and amount and discounting them to present value, they are added to arrive at total life-cycle costs for each alternative:


LCC = I + Repl — Res + E + W + OM&R + O

LCC = Total LCC in present-value (PV) dollars of a given alternative


I = PV investment costs

Repl = PV capital replacement costs

Res = PV residual value (resale value, salvage value) less disposal costs

E = PV of energy costs

W = PV of water costs

OM&R = PV of non-fuel operating, maintenance and repair costs.

O = PV of other costs (e.g., contract costs)


D. Supplementary Measures

Supplementary measures of economic evaluation are


  • Net Savings (NS),

  • Savings-to-Investment Ratio (SIR),

  • Adjusted Internal Rate of Return (AIRR),

  • Simple Payback (SPB) or

  • Discounted Payback (DPB).

All supplementary measures are relative measures, i.e., they are computed for an alternative relative to a base case.


NS = Net Savings: operational savings less difference in capital investment costs

SIR = Savings-to-Investment Ratio: ratio of operational savings to difference in capital investment costs

AIRR = Adjusted Internal Rate of Return: annual yield from an alternative over the study period, taking into account reinvestment of interim returns at the discount rate.

SPB = Simple Payback: time required for the cumulative savings from an alternative to recover its initial investment cost and other accrued costs, without taking into account the time value of money.

DPB = Discounted Payback: time required for the cumulative savings from an alternative to recover its initial investment cost and other accrued costs, taking into account the time value of money

E. Evaluation Criteria

  • Lowest LCC (for determining cost-effectiveness)

  • NS > 0 (for determining cost-effectiveness)

  • SIR > 1 (for ranking projects)

  • AIRR > discount rate (for ranking projects)

  • SPB, DPB <>

F. Uncertainty Assessment in Life-Cycle Cost Analysis
Decisions about investments typically involve a great deal of uncertainty about their costs and potential savings. Performing an LCCA greatly increases the likelihood of choosing a project that saves money in the long run. Yet, there may still be some uncertainty associated with the LCC results. LCCAs are usually performed early in the design process when only estimates of costs and savings are available, rather than certain dollar amounts. Uncertainty in input values means that actual outcomes may differ from estimated outcomes.

There are techniques for estimating the cost of choosing the "wrong" project alternative. Deterministic techniques, such as sensitivity analysis or breakeven analysis, are easily done without requiring additional resources or information. They produce a single-point estimate of how uncertain input data affect the analysis outcome. Probabilistic techniques, on the other hand, quantify risk exposure by deriving probabilities of achieving different values of economic worth from probability distributions for input values that are uncertain. However, they have greater informational and technical requirements than do deterministic techniques. Whether one or the other technique is chosen depends on factors such as the size of the project, its importance, and the resources available. Since sensitivity analysis and break-even analysis are two approaches that are simple to perform, they should be part of every LCCA.



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July 23, 2007

Alcohol Losses and Recovery Estimation

This is with reference to my previous log on this topic.
Background

Alcohol is stored in conventional storage tanks at site, which are non-insulated & low pressure fixed roof tanks. In this kind of storage system, there are three different types of losses of stored liquid.

1. WORKING LOSS

Losses due to displacement of inner air space during filling & evacuation. The material is lost each time during filling while fresh air intake results in additional evaporation inside the tank to maintain its partial pressure of liquid in vapor space.

2. BREATHING LOSS
Losses due to contraction and expansion of vapor space due to variation in day – night temperature. This also causes similar effect as explained above in item 1.

3. LOSSES DUE TO HEAT GAIN
Due to difference in ambient temperature & bulk liquid temperature, the material stored gets energy input through radiative & convective heat transfer from atmosphere. This is significant energy gain by the system compared to other two losses explained above.

Assumptions

We have assumed following parameters during this study.

1. All tanks (A, B, C, D, E, F, G, H, Q, and R) shall be used throughout the year.

2. The liquid height is 70% throughout the year.

3. Ambient temperature for the day & night is considered separately based on data from IMD Bareilly.

4. Daytime temperature is considered for 8 hours while night temperature is considered for 16 hours.
5. Conduction resistance is considered negligible for CS, which is much lower, compared to convective transfer coefficients.

Calculation Method

Breathing losses and working losses were estimated based on detailed EPA method described in AP-42 compilation of air pollutant emission factor Vol-1 by US Environmental Protection Agency.

Heat Losses were estimated based on Eq-6, 7 & 4 page-235 from ‘Process Energy Conservation’ by Richard Greene.

Steps

1. This is the first step to calculate storage tank losses i.e. list out all the tanks with dimensions and average liquid level in each tank separately.



2. Now find out the average temperatures for Day & Night for each month separately as listed below in our case.




3. Now assume a sun temperature & calculate vapor composition, Specific heat & latent heat of vapor mix. If it is pure solvent its easier. In my case it was Ethanol & water mix.

4. Assume interface temperature at tank walls & calculate heat transfer coefficient. I can provide worksheet & formula reference if anybody needs it.

5. Calculate losses & summarize them as below.

6. This will give you loss table for day & night separately so you need no of tanks x 2 worksheets for calculating these losses.



7. Now simply calculate possible recovery by condensation. I did it @ 12°C chilled water.




Results
Based on detailed calculation for each month, it was identified that the total alcohol losses from all storage tanks are in the range of ~715 TPA. The breakup of these losses is given below.



  1. Breathing Losses - 34 TPA

  2. Working Losses - 24 TPA

  3. Heat Losses - 654 TPA

  4. Total Losses - 712 TPA

  5. Recovery - 568 TPA

We can economically recover ~568 TPA (~80%) of ethanol by condensing vent vapors using chilled water of 12 °C.

The cost of this operation was ~ Rs. 1500 / Te of alcohol with a net saving of Rs. 105 Lac /Year.

Comparison with absorption system.

When using absorber I could plan to recover >98% alcohol compared to 80-81% using vent condenser saving additional Rs. 40 Lac / year.

The cost of recovery was also lower due to higher power consumption for chillers. The absorber can be designed to target ~higher alcohol concentration at the bottom of column. We finalized it at 21% due to total economics of recovering it later.

This is not only important from economics point of view but is very critical from stringent Environmental norms.

So I prefer this solution when you are having a pure solvent the only judgment needed is to minimize “after processing” cost which depends on different setups in different industries.



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July 21, 2007

Dissatisfied Chemical Engineers

After reading about the opportunities available to chemical engineers, employers might want to think about making their current employees a bit happier if they don’t want to lose them to competitors. According to Chemical Engineering’s online “Talk to Us” survey on job satisfaction, most of the 74 respondents found their jobs to be mediocre.

When asked about overall satisfaction rates, only 13.5% considered themselves to be completely satisfied with their jobs. While the majority, 25.7%, rated their overall satisfaction to be a “3” on a scale of “1 to 5,” with “5” being completely satisfied and “1” being completely unsatisfied.



Another 6.8% said they were completely unsatisfied. The outlook is worse when it comes to professional mobility, as only 9.5% said they were completely satisfied with this aspect of their job and almost 15% (14.9%) of respondents said they were completely unsatisfied. Less than stellar responses were also recorded regarding compensation. Only 12.2% were completely satisfied with the compensation they receive. Again, in both the professional mobility and compensation categories, the majority, 27% and 27%, respectively, rated their satisfaction as a “3” on a scale of “1 to 5.”

The only facet of job satisfaction that scored slightly higher than an average “3,” was intellectual stimulation, in which the majority, 25.7%, of respondents rated their satisfaction a close-to-completely satisfied “4” on the scale.


One respondent summed up the findings by saying, “The job is good for a select few, but one must really have a passion for it to keep motivated.”

Source: Chemical Engineering July-2007

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July 20, 2007

Learning Tips

Phrases for Successful Life
  1. Think – there must be a better way.

  2. Problems are only solutions in disguise.

  3. Learn by Listening ….. Understand by reflecting.

  4. Speech is better but quiet is intelligence.

  5. There is no right way to do something wrong.

  6. Making excuse does not hurt anybody, but your self.

  7. A liar is not believed when he speaks the truth.

  8. A man’s reach should not exceed his grasp.

  9. Strong convictions precede great actions.

  10. Arrogance is the quicksand of success.

  11. The greatest loss is the loss of self – confidence.

  12. Learn to say " NO ".

  13. Success has made failures of many man.

  14. Experience is one thing you can’t get for nothing.

  15. Organise Yourself well to have more time to do things you love to do.

  16. You cannot be anything if you want to be everything.

  17. Don’t start something which you cannot stop.

  18. Of all the things you wear, your expression is the most important.

  19. There’s plenty of room at the top, but there’s no room to sit down.

  20. Admitting you’re wrong is a modest way showing you’ve grown a little wiser.

  21. Ships are safer in the harbour, but they are not meant for that purpose.

  22. Some people pay so much attention to their reputation that they loss their character.

  23. When confessed, the sin becomes less since it becomes the truth.

  24. Even if you’re on the right track, you’ll get run over if you just sit there.

  25. At the start of your career, what you learn is more important that what you earn.

  26. There is no indigestion worse than that which comes from having to eat your own wards.

  27. A vacation should be just long enough for the boss to miss you and not long enough for him to discover how well he can get along without you.

  28. The fire you kindle for your enemy burns yourself more than him.

  29. Either I will find a way or make one.

  30. If it were not for the rock in the bed , the stream would have no song.

  31. There are two ways of spreading light: to be the candle or the mirror that reflects it.

  32. Always tell yourself: The difference between running a business and running a business is “I”.

  33. A wise man is one who forgets the fault of others, but always remembers his own.

  34. Cut your social functions where your substitute will be equally good and no one will miss you.

  35. It is not only machinery that becomes obsolete. One has to guard against obsolescence of the mind.

  36. Many a live wire would be dead except for his connections.

  37. Success isn’t the opposite of failure. A runner may come is last , but if he beats his Record , he succeeds.

  38. A man is not hurt so much by what happens as by his opinion of what has happened.

  39. Other men see things as they are and ask, “why”. I see things that never were and ask,
    “Why not?”.

  40. A fundamental requirement for success: humility.

  41. Dare to dream –dare to try-dare to fail- dare to success.

  42. Watch your thoughts- they become your words.

  43. Watch your words- they become your actions.

  44. Watch your action- they become your habits.

  45. Watch your habits- they become your character.

  46. Don’t be afraid to ask dumb questions: they’re more easily handled than dumb mistakes.

  47. Why are we so polite to those we don’t know, and so rude and crude to those we love?.

  48. When all of us think alike, no one is thinking.

  49. When the blind man carries the lame, both go forward.

  50. Praise in public; reprimand in private.

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Reduce Losses from Storage Tanks

Today I was reading a question regarding reduction in losses from large storage tanks for solvents. The existing system was having ~300 tanks at set pressure of 200 mmWC with vent condensers. 10°C chilled water is used for chilling in those vent condensers with vent setting of non condensable at 300 mmWC.

Few experts on the forum suggested that use 2-3°C chilled water to reduce the vent losses and properly size the condensers for improved heat transfer.

Any comment……………Before I proceed…….If U really have different things in mind let me know & I offer a job in technical services department of my company.
(This offer is for readers from India only for Chemical Engineering Graduates with 0 to 8 years experience)

I will post my solution which I have implemented here cost effectively on Monday.
___________________________________________________________________
Disclaimer: I do not guarantee the job offer unless the candidate qualifies other parameters of selection procedure.

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China: Growing Fast

By 2010 purchases of centrifugal pumps in China will rise to over $5 billion, surpassing the U.S., whose purchases are projected at under $4.9 billion. These are the latest forecasts in Pumps:

The top ten purchasers in 2010 will include primarily Asian and European countries:

2010 Projected Centrifugal Pump Purchases ($ Millions)
China: 5,149
United States: 4,886
Japan: 1,595
India: 1,092
Germany: 1,085
France: 764
United Kingdom: 742
Russia: 742
Brazil: 740
Italy: 680
South Korea: 640

Municipal wastewater represents the largest application in China and in the world, driven by the migration of one billion people in Asia from the countryside to cities. The chemical industry is the second largest application in China and in the world.

Power is the third largest application. In 2007 China became the leading operator of coal-fired power plants in the world. By 2011 it is projected that China will be operating twice the coal-fired capacity of the U.S. and more than all of Europe combined.

China is developing the manufacturing capability to move beyond the standard water pumps to offer pumps for critical applications. The U.S. will remain the second largest purchaser of pumps even though there will be a slowdown in refining and oil and gas production. Coal-fired power, ethanol and other growth areas will compensate for the segments which are not growing. The outlook in Japan is looking brighter and it will remain the third largest purchaser.
Source: World Markets an online report published by the McIlvaine Co.

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July 19, 2007

Butanol Vs Ethanol Vs Future..............????


Bio - Butanol

  • Can be made from natural sugar or starch including waste materials.
  • Costs less than ethanol.
  • Has 92% of the energy content of gasoline.
  • Mixes well with gasoline or ethanol.
  • Evaporates more slowly than either gasoline or ethanol.
  • Can be used in place of gasoline with no engine or fuel system changes.
  • Makes usable hydrogen as a by product.
  • Higher energy content (110,000 Btu’s per gallon for butanol vs. 84,000 Btu per gallon for ethanol). Gasoline contains about 115,000 Btu’s per gallon.
  • Butanol is six times less “evaporative” than ethanol and 13.5 times less evaporative than gasoline, making it safer to use as an oxygenate.
  • Butanol can be shipped through existing fuel pipelines where ethanol must be transported via rail, barge or truck.
  • Butanol can be used as a replacement for gasoline gallon for gallon e.g. 100%, or any other percentage. Ethanol can only be used as an additive to gasoline up to about 85% and then only after significant modifications to the engine. Worldwide 10% ethanol blends predominate.

Its now has trade names of BioButanol, Butyl-Fuel, Butafuel and others.

Like ethanol, it is an alcohol that can be made from corn. It can also be made, at lower cost, from other raw materials.

Butanol is produced efficiently from sugar or starch by anaerobic fermentation. As example, it can use corn, grain, potatoes, sugar beets, grass, leaves, trees, kudzu or agricultural waste.

A recent technology breakthrough, made in Ohio, allows butanol to be made for as little as 85¢ a gallon from waste materials.

In this country, there is a pilot plant under construction to make butanol from milk sugar using waste from making cheese. It solves a waste disposal problem for cheese makers and makes fuel that can replace gasoline gallon for gallon.

In Great Britain, DuPont and BP are working together to convert an ethanol plant to butanol production. They will be using sugar beets as the raw material.

Does it really work as a motor fuel? Yes, it was demonstrated during the summer of 2005. A stock 1992 Buick Park Avenue was driven for 10,000 miles around the USA using 100% Butanol as fuel. There were no problems. The was still running strong at the end of the tour.

The Buick was tested for pollution emissions by 10 of the states that it visited. It passed the tests in all 10 states. Its tail pipe emissions were much cleaner than any gasoline fueled engine.

In actual driving conditions, butanol has a strong power and torque content. Drivers will use a lighter foot on the accelerator and hold a higher gear longer.

The Buick had mileage checks that ranged from 24 to 28 mpg on butanol. The same car had averaged 22 mpg using gasoline. So it has got higher efficinecy by 10-30%.

Butanol is also being evaluated for use in Bio Diesel mixes and as a fuel for jet aircraft.

You will be hearing more about the bio butanol as development continues. It has the potential of reducing our dependence on imported fossil fuels. In addition, it can reduce the stress on the environment.



I will put my comments on different Bio Fuels later..............





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July 18, 2007

Recovery of Alcohols from Dilute Solutions

I have recently found that Hexyl Acetate is a very good solvent for the liquid liquid extraction of alcohols from their dillute solutions.

This is possible because Hexyl Acetate is insoluble in water & have very good affinity for alcohols.

You can try it at lab scale for your system. However I feel that it will be good to use it if effluent is having >4% alcohol.

This will be much cheaper in comparison to distillation.


Hope it is useful for you........
You can add more solvents for such technologies.



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Suction Vs Discharge Gas Flow

Today I was reading a very interesting discussion on one of the famous forums at Cheresources.

This was really interesting. Newcomers should learn these useful things to avoid confusing states and hence it enables them for better decision making skills.


Why there is a difference in the measured suction flow & discharge flow of a blower (No Spill Back or antisurge or recycle is there). She got Suction flow as 62000 Nm3/Hr and discharge as 48000. How it is possible??????????


I would rather focus on other aspect of it - the practical one.


How the flowmeters work...................? The root cause of this problem lie in this question.


Flowmeters are actually measuring (DP type - Orifice etc) differential pressure across the tappings used for Orifice. Now in case of compressible fluid flow the most important thing is its density or in general terms its P, T, Mol Wt & Compressibility Z (for high pressure systems you can ignore Z for low pressure systems as it doesnt vary too much).


When we use these flow meters they usually experience different P & T and sometimes if gas is not fixed MW also vary. Therefore, at same mass flow rate also the DP across flowmeter will be different due to change in its density.


Now if we convert this measured DP to flow value based on its design DP & flow range which is usually considered (or fed in the system) by instt people, it will give a wrong indication.


Why??????????


Becasue generally spec sheet is mentioned in Nm3 flow not in terms of actual M3 flow. So if spec sheet is having actual M3 flow than above conversion will also give actual M3 flow and would be correct..........Here comes next practical aspect...............


But indication on DCS is provided in Nm3 generally without thinking & checking all the units.............


So we must be careful for our actions when we install any flowmeter............Instt should consult technical services deptt for parameters correction.


Further there should be an standard practice for providing online compensation of P & T in each compressible fluid flowmeter for better understanding...........because uncompensated flow lead to some wrong decisions in emergencies, startup etc when variations are large compared to design values.


In the above case, it seems that both the flows are Actual M3 flows, when converted to Nm3 they are closer than given figures...........Its just a possibility.


Hope it is useful for you?????????


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Energy Efficient Ethanol Production

Chemical engineers Richard D. Offeman and George H. Robertson at the ARS Western Regional Research Center in Albany, Calif., think it may be possible to cut energy costs by using a series of specially designed permeable plastic sheets, or membranes, to produce ethanol from fermented broths of corn, or straw and other kinds of biomass feedstocks.

The technology will help to address the serious concern regarding the energy efficiency of bioethanol production, according to Robert L. Fireovid, ARS national program leader for process engineering and chemistry, Beltsville, Md.

The researchers' invention, called a spiral-wound liquid membrane module, could potentially replace the widely used process of distilling ethanol from fermentation broths. The module offers ethanol producers the important advantage of combining two separation processes, extraction and membrane permeation, in one piece of equipment.

With further research and development, the module would require less energy than distillation. Today, energy costs are ethanol producers' second largest expense; feedstocks are first.

In brief, the fermentation broth—typically containing about five to 12 percent ethanol—would travel through a sandwich-like configuration of membranes and mesh sheets, called spacers, that keep the membranes separate from each other. One membrane has a solvent in its pores that extracts the ethanol from the broth. A second membrane, with the help of a vacuum, pulls the ethanol out of the solvent. The ethanol-and-water vapor that results is then, in other equipment, condensed into an ethanol-rich liquid.

The scientists have applied for a patent. They now plan to build and fine-tune a prototype, then turn it over to a membrane manufacturer for further development before commercialization.

Already, some ethanol producers have expressed interest in the invention.

The device has other potential uses, such as cleaning up wastewater or treating natural gas for home use.
Source: US Deptt of Agriculture

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July 07, 2007

Water As Fuel

Forget cars fuelled by alcohol and vegetable oil. Before long, you might be able to run your car with nothing more than water in its fuel tank. It would be the ultimate zero-emissions vehicle.
While water, plain old H2O, is not at first sight an obvious power source, it has a key virtue: it is an abundant source of hydrogen, the element widely touted as the green fuel of the future. If that hydrogen could be liberated on demand, it would overcome many of the obstacles that till now have prevented the dream of a hydrogen-powered car becoming reality. Producing hydrogen by conventional industrial means is expensive, inefficient and often polluting. Then there are the problems of storing and transporting hydrogen. The pressure tanks required to hold usable quantities of the fuel are heavy and cumbersome, which restricts the car's performance and range.


Tareq Abu-Hamed, at the University of Minnesota, and colleagues at the Weizmann Institute of Science in Rehovot, Israel, have devised a scheme that gets round these problems. By reacting water with the element boron, their system produces hydrogen that can be burnt in an internal combustion engine or fed to a fuel cell to generate electricity. "The aim is to produce the hydrogen on-board at a rate matching the demand of the car engine," says Abu-Hamed. "We want to use the boron to save transporting and storing the hydrogen." The only by-product is boron oxide, which can be removed from the car, turned back into boron, and used again. What's more, Abu-Hamed envisages doing this in a solar-powered plant that is completely emission-free.


Simple chemistry


The team calculates that a car would have to carry just 18 kilograms of boron and 45 litres of water to produce 5 kilograms of hydrogen, which has the same energy content as a 40-litre tank of conventional fuel. An Israeli company has begun designing a prototype engine that works in the same way, and the Japanese company Samsung has built a prototype scooter based on a similar idea.

The hydrogen-on-demand approach is based on some simple high-school chemistry. Elements like sodium and potassium are well known for their violent reactions with water, tearing hydrogen from its stable union with oxygen. Boron does the same, but at a more manageable pace. It requires no special containment, and atom for atom it's a light material. When all the boron is used up, the boron oxide that remains can be reprocessed and recycled.


Abu-Hamed and his team are not the first to investigate hydrogen-on-demand vehicles. The car giant DaimlerChrysler built a concept vehicle called Natrium (after the Latin word for sodium, from which the element's Na symbol is drawn), which used slightly more sophisticated chemistry to generate its hydrogen. Instead of pure water as the source of the gas, it used a solution of the hydrogen-heavy compound sodium borohydride. When passed over a precious-metal catalyst such as ruthenium, the compound reacts with water to liberate hydrogen that can be fed to a fuel cell. It was enough to give the Natrium a top speed of 130 kilometres per hour and a respectable range of 500 kilometres, but DaimlerChrysler axed the project in 2003 because of difficulties in providing the necessary infrastructure to support the car in an efficient, environmentally friendly way.


Engineuity, an Israeli start-up company run by Amnon Yogev, a former Weizmann Institute scientist, is working on a similar strategy, but using the reaction between aluminium wire and water to generate hydrogen. In Engineuity's design, the tip of the metal wire is ignited and dipped into water to begin splitting the water molecules. The liberated hydrogen is piped into the engine alongside the resulting steam, where it is mixed with air and burnt. Engineuity is looking for investors to pay for a prototype, and claims it will be able to commercialise its idea "in a few years' time". The US company PowerBall Technologies envisages a hydrogen-on-demand engine containing plastic balls filled with sodium hydride powder that are split to dump the contents into water, where it reacts to produce hydrogen.

Abu-Hamed says the generation of hydrogen for his team's engine would be regulated by controlling the flow of water into a series of tanks containing powdered boron. To kick-start the reaction, the water has to be supplied as vapour heated to several hundred degrees, so the car will still require some start-up power, possibly from a battery. Once the engine is running, the heat generated by the highly exothermic oxidation reaction between boron and water could be used to warm the incoming water, Abu-Hamed says. Alternatively, small amounts of hydrogen could be diverted from the engine and stored for use as the start-up fuel. Water produced when the hydrogen is burnt in an internal combustion engine or reacted in a fuel cell could be captured and cycled back to the vehicle's tank, making the whole on-board system truly zero-emission.

Hydrogen-on-demand, whether from water or another source, could address two of the big problems still holding back the wider use of hydrogen as a vehicle fuel: how to store the flammable gas, and how to transport it safely. Today's hydrogen-fuelled cars rely on stocks of gas produced in centralised plants and distributed via refuelling stations in either liquefied or compressed form. Neither is ideal. The liquefaction process eats up to 40 per cent of the energy content of the stored hydrogen, while the energy density of the gas, even when compressed, is so low it is hard to see how it can ever be used to fuel a normal car.


Hydrogen-on-demand would not only remove the need for costly hydrogen pipelines and distribution infrastructure, it would also make hydrogen vehicles safer. "The theoretical advantage of on-board generation is that you don't have to muck about with hydrogen storage," says Mike Millikin, who monitors developments in alternative fuels for the Green Car Congress website. A car that doesn't need to carry tanks of flammable, volatile liquid or compressed gas would be much less vulnerable in an accident. "It also potentially offsets the requirements for building up a massive hydrogen production and distribution infrastructure," Millikin says.

There is a potentially polluting step that has to be tackled. "You'll need an infrastructure to produce and distribute whatever the key elements of the generation system might be," Millikin warns. While Abu-Hamed's scheme still requires a distribution network and reprocessing plant, he has devised an ingenious plan that will allow the spent boron oxide to be converted back to metallic boron in a pollution-free process that uses only solar energy. Heating the oxide with magnesium powder recovers the boron, leaving magnesium oxide as a by-product. The magnesium oxide can then be recycled by first reacting it with chlorine gas to produce magnesium chloride, from which the magnesium metal and chlorine can then be recovered by electrolysis.


Solar source

The energy to drive these processes would ultimately come from the sun. The team calculates that a system of mirrors could concentrate enough sunlight to produce electricity from solar cells with an efficiency of 35 per cent. Overall, they say, their system could convert solar energy into work by the car's engine with an efficiency of 11 per cent, similar to today's petrol engines.

Experts are sceptical that we'll be seeing cars running on water any time soon. "It's not the kind of thing you're going to see appearing in a car in five or even ten years' time," says Jim Skea, research director at the UK Energy Research Centre in London. For example, DaimlerChrysler is now focusing its efforts on cars running on compressed hydrogen because filling stations that supply it already exist in some places.

Proponents of cars that run on water are banking that long term the idea will win out. Engineuity's Yogev claims the running costs will be comparable to those of today's petrol engines and expects to have a prototype built within three years.

My other car runs on water? Don't bet against it.


Its a long way to realize these technologies in practice..........

They are not so easy in actual applications..........at least for commercial transportation etc., though Industry can build up on these Ideas due to infrastructures available with them.


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Electricity from Waste water

Researchers are studying the viability of creating electricity from microbes that are continuously fed with wastewater. If this technology reaches a proven and commercially realizable point, we could see a new edge technology in power generation.

Researchers from the University of Washington in St. Louis have been working on microbial fuel cell that generates electricity from wastewater. The science behind this technology is quite simple. Wastewater contains, among other things, organic matter. This organic matter can serve as a feedstock for many bacterial reactions. If an electrode is placed within the system where bacteria can develop and colonize, then a fuel cell can be made. As the bacteria feeds on the organic material in the wastewater, they release electrons. These electrons are collected in the anode, which then move to the cathode (transferred through copper wires). When electrons are released and made to move, then electricity is generated.

According to current research, the present level of technology on microbial energy generation is around 160 watts per cubic meter of wastewater. The goal is to increase this power output ten times. When that happens, microbial fuel cell systems would provide households with enough renewable energy without much investment. Money and certainly energy, would then be saved from going down the drain.
Source: Science daily

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Safeguard your Compressors

Generally almost every industry face the problem of failures / corrosion / pitting in compressors internals due to presence of mainly mositure while handling any gas coming out through a wet system or air.
The Reason

1. Condensation in the line between the separator and the compressor.

2. Liquid from the separator due to fine mist carryover with the gas.

  • For suction line there are two possibilities either to provide good insulation and/or heat traced or to provide a condensate boot with a drain line for intermittent automatic draining through a drain valve which operates on gravity.
  • From generally accepted rules, be sure that the separator is properly sized. If the separator does not include a mesh pad, consider installing one to see if this helps. You also may want to install a mist eliminator in the line leading to the compressor (and change it at least twice a year).
However, my experience with this in case of a reciprocating compressor for CO2 gas is that the design of separator internals are very important aspect for better separation efficiency. Many configurations are possible from easiest one being the downward inlet pipe with baffles or tangential entry to the complex ones as shown in the graphics below.




I have improved the efficiency of our system by first putting a 45° downward angled baffle at the front of inlet pipe, which knocked of most of the mositure/mist by impingement and then channelized the gas flow by reversing its direction 2 times before it passes through mesh pad.

The maintenance frequency for the compressor reduced from 2 months to more than a year.


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Carnot Cycle - An Insight

Carnot - Can OR Cannot???????


This is in continuation of my previous article on 'Thermodynamics of Thermal Cycles' & is related to practical aspects of it.

All standard heat engines (steam, gasoline, diesel) work by supplying heat to a gas, the gas then expands in a cylinder and pushes a piston to do its work. The catch is that the heat and/or the gas must somehow then be dumped out of the cylinder to get ready for the next cycle.


We consider the standard Carnot-cycle machine having a piston moving within a cylinder, and having the following characteristics:
  • A perfect seal, so that no atom escape from the working fluid as the piston moves to expand or compress it..............Wear & tear cannot be eliminated.
  • Perfect lubrication, so that there is no friction...........Impractical.
  • An ideal-gas for the working fluid................Not true at working conditions of pressure & temperature.
  • Perfect thermal connection at any time either to one or to none of two reservoirs, which are at two different temperatures, with perfect thermal insulation isolating it from all other heat transfers......................Cannot be achieved practically.
  • The piston moves back and forth repeatedly, in a cycle of alternating "isothermal" and "adiabatic" expansions and compressions, according to the PV diagram shown below:
This is basically
  1. A high temperature Isothermal Expansion from A to B. - Heat is Supplied to the engine.
  2. An Adiabatic expansion cooling down from B to C.
  3. A low temperature Isothermal compression from C to D - Heat Removal step.
  4. Adiabatic compression from D to A - work performed on fluid.

Carnot cycle works as an engine if heat is absorbed from A to B and rejected at C to D doing some useful work. It works as a heat pump if it is motor driven.

Isothermal Expansion

So the first question is: how much work is done by an isothermally expanding gas? Taking the temperature of the heat reservoir to be Th (h for hot), the expanding gas follows the isothermal path PV = n R Th in the (P, V) plane.

Hence the work done in expanding isothermally from volume Va to Vb is the total area under the curve between those values,

W = n R Th Ln(V2/V1)


Since the gas is at constant temperature Th, there is no change in its internal energy during this expansion, so the total heat supplied must be, the same as the external work the gas has done.


In fact, this isothermal expansion is only the first step: the gas is at the temperature of the heat reservoir, hotter than its other surroundings, and will be able to continue expanding even if the heat supply is cut off. To ensure that this further expansion is also reversible, the gas must not be losing heat to the surroundings. That is, after the heat supply is cut off, there must be no further heat exchange with the surroundings, the expansion must be adiabatic.

Adiabatic Expansion

The work done in an adiabatic expansion is like that done in allowing a compressed spring to expand against a force—equal to the work needed to compress the spring in the first place, for a perfect spring, and an adiabatically enclosed gas is essentially perfect in this respect. In other words, adiabatic expansion is reversible. To find the work the gas does in expanding adiabatically from Vb to Vc, say, the above analysis is repeated with the isotherm replaced by the adiabatic equation PV^^k = Constant where k is adiabatic coefficient.

W = Pb Vb^^k * (Vc^^1-k - Vb^^1-k) / (1-k)

OR

W = (Pc Vc - Pb Vb) / (1-k)

(I do not know how to use exponent in this blogger thing....if anybody can help me he is welcome).

We’ve looked in detail at the work a gas does in expanding as heat is supplied (Isotherm) and when there is no heat exchange (adiabatically). These are the two initial steps in a heat engine, but it is equally necessary for the engine to get back to where it began, for the next cycle. The general idea is that the piston drives a wheel,which continues to turn and pushes the gas back to the original volume.



Download an animated version of Carnot Engine here.

The PV diagram for the complete cycle is given below.




Efficiency of the Carnot Engine
In a complete cycle of Carnot’s heat engine, the gas traces the path abcd. The important question is: what fraction of the heat supplied from the hot reservoir (along the red top isotherm) is turned into mechanical work? This fraction is called the efficiency of the engine.

The work output along any curve in the (P, V) plane is just --the area under the curve, but it will be negative if the volume is decreasing! So the work done by the engine during the hot isothermal segment is the area abfh, then the adiabatic expansion adds the area bcef, but as the gas is compressed back, the wheel has to do work on the gas equal to the area cdge as heat is dumped into the cold reservoir, then dahg as the gas is recompressed to the starting point.

The bottom line is that the total work done by the gas is the area bounded by the four paths: the curved "parallelogram" in the picture above. We could compute this area by finding P dV for each segment, but that is unnecessary—on completing the cycle, the gas is back to its initial temperature, so has the same internal energy. Therefore, the work done by the engine must be just the difference between the heat supplied at Th and that dumped at Tc.

Now the heat supplies along the initial hot isothermal path ab, equal to the work done along that leg, is (from the paragraph above on isothermal expansion):

Qh = n R Th Ln(Vb/Va)

and the heat dumped into the cold reservoir along cd is


Qc = n R Tc Ln(Vc/Vd)

Finally after some simple math

Efficiency = 1 - Tc / Th

It can be easily proved by second law of thermodynamics that no engine can be more efficient than carnot engine. As I have already shown in my previous article that Ideal carnot cannot go beyond 80% efficiency given the above assumptions are true, while practical combined efficiency of all mechanical system is ~40%. Thus, overall efficinecy drops to ~32%.

Clearly the major contributor is mechanical losses not thermodynamic losses. Hence, as per my analysis this is true only for said four step cycle and for thermodynamic efficiency operating between Th & Tc. Now engines have been devised with different no of thermodynamic steps, therefore reducing the total mechanical losses and improving overall system efficiency.

So if we can device a system where each mechanical component can either be improved or can be eliminated we can significantly increase the efficiency of overall cycle. (Fornuately it has been done, Read it here.....Waste Heat driven Engine)

However the above technology is still doubtful about its suitability for large size machines where a true HEAT ENGINE would be replaced by it.

Therefore, til that time we have to consider different cycles for improving the efficiency as I would present it in my next papers on Thermodynamics of heat engine ( Probably with exergy if I get some more time).


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July 04, 2007

Longest English Word - Again a Protein - 1,89,189 Letter

Thanks Egon for your comment,

While posting the earlier protein Enaptin's full name I found that this one is longest & I am sure this cant be beaten.

Chemical Short Name - Titin

Type - Protein

Chemical Formula: C132983H211861N36149O40883S693

Letters: 1,89, 819


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July 03, 2007

The longest chemical name, 64,060 letters

Featured today in Wikipedia's newest pages, Methionylalanylthreonyl...leucine is a chemical name for enaptin, a nuclear envelope protein found in human myocytes and synapses, which is made up of 8,797 amino acids. Hope this won't be a dupe, this will be hard to search for.

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180 Food Factories shut down for use of illegal chemicals

This is happening in China today. This has happened in China as far as I know for at least 10-20+ years. I'm surprised that the media is only paying attention to this story now. I know it sounds rather paranoid, but it IS possible to avoid products 'Made in China'. Even towels made in China can expose a person to illegal chemicals!

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Common Eco-Myth: Sodium Lauryl Sulfate (SLS) Causes Cancer

"One such misperception that has managed to persist in the public domain over the last few years is the perceived carcinogenic risk posed by sodium lauryl sulfate, a chemical commonly found in beauty care products. Despite strong evidence to the contrary, including an article published by the American Cancer Society definitively positing no link...

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Chaeper Solar Power

Dr Wayne Campbell and researchers in the Massey University centre have developed a range of coloured dyes for use in dye-sensitised solar cells.

The synthetic dyes are made from simple organic compounds closely related to those found in nature. The green dye is synthetic chlorophyll derived from the light-harvesting pigment plants use for photosynthesis. Other dyes being tested in the cells are based on haemoglobin, the compound that give blood its colour.
Dr Campbell says that unlike the silicon-based solar cells currently on the market, the 10 x 10 cm green demonstration cells generate enough electricity to run a small fan in low-light conditions – making them ideal for cloudy climates. The dyes can also be incorporated into tinted windows that trap to generate electricity.

He says the green solar cells are more environmentally friendly than silicon-based cells as they are made from titanium dioxide – a plentiful, renewable and non-toxic white mineral obtained from sand. Titanium dioxide is already used in consumer products such as toothpaste, white paints and cosmetics.

“The refining of pure silicon, although a very abundant mineral, is energy-hungry and very expensive. And whereas silicon cells need direct sunlight to operate efficiently, these cells will work efficiently in low diffuse light conditions,” Dr Campbell says.

“The expected cost is 1/10th of the price of a silicon-based solar panel, making them more attractive and accessible to home-owners.”

The Centre’s new director, Professor Ashton Partridge, says they now have the most efficient porphyrin dye in the world and aim to optimise and improve the cell construction and performance before developing the cells commercially.
“The next step is to take these dyes and incorporate them into roofing materials or wall panels. We have had many expressions of interest from companies,” Professor Partridge says.

He says the ultimate aim of using nanotechnology to develop a better solar cell is to convert as much sunlight to electricity as possible. “The energy that reaches earth from sunlight in one hour is more than that used by all human activities in one year”.
The solar cells are the product of more than 10 years research funded by the Foundation for Research, Science and Technology.
Source: Massey University

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Energy Saving Tips-2

Tips in Day to Day Life
  1. In many cases you can use lower wattage bulbs and get same amount of light. Look for lumens on the bulb (CFL) & not for watts. Lumen indicates the brightness while power indicates eenrgy required to illuminate the area.
  2. Always plan bulb location in such a way that the light is not hindered by any other room fixture.

  3. White light is more comfortable than any other light for reading & day to day use. So should consider it in studies, drawing room etc. Other types can be considered for infrequently used areas e.g. toilet, bathroom etc.
  4. Install photoelectric controls for outdoor lighting.
  5. Choose light colors in the rooms for better reflection, becasue dark colors absorb light & need more wattage for same illumination.
  6. Use good quality reflector & you can save lot of energy due to higher reflection. This can bring it down by ~33% if designed properly i.e. selection of reflector, selection of bulb, location etc.

  7. Use dimmer controls for reducing energy consumption whenever possible.
  8. Try to locate AC unit on the north side of house to avoid direct sunlight.

  9. Use sun screens on window glasses to avoid radiation heat.

  10. AC thermostat setting should be ~24°C which is reasonably good & comfortable temperature everywhere.

  11. Use low wattage lighting in the rooms to avoid unnecessary load on AC.

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Engineers Find Way To Make Ethanol, Valuable Chemicals From Waste Glycerin

With U.S. biodiesel production at an all-time high and a record number of new biodiesel plants under construction, the industry is facing an impending crisis over waste glycerin, the major byproduct of biodiesel production.
New findings from Rice University suggest a possible answer in the form of a bacterium that ferments glycerin and produces ethanol, another popular biofuel.
"We identified the metabolic processes and conditions that allow a known strain of E. coli to convert glycerin into ethanol," said chemical engineer Ramon Gonzalez. "It's also very efficient. We estimate the operational costs to be about 40 percent less that those of producing ethanol from corn."

Gonzalez said the biodiesel industry's rapid growth has created a glycerin glut. The glut has forced glycerin producers like Dow Chemical and Procter and Gamble to shutter plants, and Gonzalez said some biodiesel producers are already unable to sell glycerin and instead must pay to dispose of it.

"One pound of glycerin is produced for every 10 pounds of biodiesel," said Gonzalez, Rice's William Akers Assistant Professor in Chemical and Biomolecular Engineering. "The biodiesel business has tight margins, and until recently, glycerin was a valuable commodity, one that producers counted on selling to ensure profitability."

Researchers across the globe are racing to find ways to turn waste glycerin into profit. While some are looking at traditional chemical processing -- finding a way to catalyze reactions that break glycerin into other chemicals -- others, including Gonzalez, are focused on biological conversion. In biological conversion, researchers engineer a microorganism that can eat a specific chemical feedstock and excrete something useful. Many drugs are made this way, and the chemical processing industry is increasingly finding bioprocessing to be a "greener," and sometimes cheaper, alternative to chemical processing.

In a review article in the June issue of Current Opinion in Biotechnology, Gonzalez points out that very few microorganisms are capable of digesting glycerin in an oxygen-free environment. This oxygen-free process -- known as anaerobic fermentation -- is the most economical and widely used process for biological conversion.

"We are confident that our findings will enable the use of E. coli to anaerobically produce ethanol and other products from glycerin with higher yields and lower costs than can be obtained using common sugar-based feedstocks like glucose and xylose," Gonzalez said.

The report in Current Opinion in Biotechnology was co-authored by postdoctoral research associate Syed Shams Yazdani. Graduate students Yandi Dharmadi and Abhishek Murarka assisted with the research. Gonzalez's research is funded by the U.S. Department of Agriculture and the National Science Foundation.
Source: Rice University & Chemical Online

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