December 29, 2008

Hydrogen Economy: Dream or Future

Hydrogen powered automobiles are a recurrent idea these days. Prototype hydrogen-powered cars are debuting in the United States, Japan and Europe. Two major issues are driving the Hydrogen Dream – Global Warming and Over-dependence on imported oil.

The idea of hydrogen economy is to utilize locally available and renewable energy sources, such as wind, solar and biomass to produce hydrogen gas. Hydrogen can then be used in fuel cells to produce electricity without producing pollution; replacing gasoline and petroleum with hydrogen would decrease the consumption of petroleum and also reduce the carbon-dioxide emissions.

BUT.. is it realistic to think that inexpensive, pollution-free hydrogen energy will be the fuel of the future?

First of all hydrogen is not at all a primary source of energy. It is always chemically bound in organic compounds or water. We require some other source like fossil fuel, nuclear reactors, hydroelectric dams, geothermal wells, wind turbines or solar panels to break the chemical bonds and hence produce free hydrogen. So basically hydrogen economy is incomplete without a primary energy source.

Well we can use electrical energy too for electrolysis of water (direct current + water = hydrogen + oxygen). But this process is highly inefficient. Only 45% of the initial energy is captured in this process.

Then there are numerous other problems attached to Hydrogen. Storing hydrogen is perhaps the greatest hurdle. Compressed hydrogen gas is the only viable approach. Carbon-fiber tanks can hold hydrogen at 10,000 psi. However, thee tanks hold only one-eighth the energy of a gasoline tank of equal size.

Moreover, compressed gas at 10,000 psi can be extremely dangerous. The energy released by the sudden rupture of a 10,000 psi tank holding 6 kg of hydrogen is equivalent to 50 sticks of dynamite!!

Even liquid hydrogen ( at -250 °C) has only one-fourth of the energy per unit volume of gasoline.

To add to the problems, hydrogen is odorless and invisible and has a wide range of flammability.

So, how realistic is the vision of the Hydrogen economy ?? And when will it occur ?? I guess some fundamental breakthroughs are necessary to make hydrogen economy a reality but one more thing.. Is Hydrogen economy the right goal ??

CHEW ON THIS TOO: - Recent Developments
Recently I came across an article - “Hydrogen Balls: a safe fuel of future”. This was about hydrogen powered cars. Thought of mentioning it here.

Hydrogen gas is stored in small balls – “ping pong” balls to overcome the risk of fire and explosion. Lass Stenmark, Uppsala University says, “By storing the gas in round, spherical form, it can withstand twice the pressure that a cylindrical form can. If the car crashes and tank breaks, the hydrogen-filled balls would just spread out and roll away, and the gas from any broken balls would just simply seep out and disappear into the atmosphere without causing harm”

Sounds simple and exciting, lets wait and see the application part !!


By Associate Writer - Nidhi Garg

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December 24, 2008

Understanding Steam Flow Meters

Energy has always been a concern for all producers / manufacturers & those who cared for it - survived all seasons, balance were extinguished by the nature. This is the law of survival.

Currently, rising prices of crude oil has affected each & every producer in many areas & therefore it is essential to understand every minute aspect of energy saving.
(Though by the time it reaches you Crude has already come down to <40$ from 140$, but doesnt matter as Energy is always beneficial for the company, for the nation, & for the Globe).


The past few years have brought a great deal of attention to energy production and use. The rising price of crude oil has affected many areas of our economy, including by such impacts as higher gasoline prices, rising jet fuel prices, and increased heating oil costs.

Steam flow measurement is important in this context because steam is widely used as a source of power in the production of electricity. In today’s power plants, heat is obtained from multiple sources. These include fossil fuels, such as coal, natural gas, or oil, as well as other sources of heat, including nuclear fuel, waste fuels, solar energy, and geothermal energy. The heat energy in these sources of heat is released, either through combustion or through a similar process. The heat is transferred to water, which generates steam. In many cases, this steam is then used to drive an electric generator. The system used to generate the steam is called a boiler.

As the costs of energy rise, many companies are looking to increase
efficiencies in their energy and power generation. As a result, more attention is being paid to steam flow measurement.

Steam flow measurement accounts for about 6 percent of the revenues from flowmeters sold in today’s $4.5 billion flowmeter market. While as many as seven different types of flowmeters can be used to measure steam flow, the vast majority of steam flow measurements are made with differential-pressure (DP) and vortex flowmeters.

1. Differential-Pressure Flowmeters
DP flow transmitters together with primary elements account for well over half of the flowmeters sold for steam flow applications. DP flow transmitters sold for steam flow have many of the same advantages and disadvantages of DP flow transmitters sold to measure liquid and gas flow. Disadvantages include pressure drop, interference with the flowstream, and wear over time. DP flow transmitters also have limited rangeability and are reliant on the square-root method for calculating flow.

On the one hand, DP flow transmitters offer some pretty compelling advantages when it comes to steam flow measurement. For example, they are relatively inexpensive and offer straightforward installation. DP flow is also the most studied and best understood method of flow measurement, and multivariable DP flow transmitters are capable of measuring more than one process variable, such as differential pressure, process pressure, and temperature, which in turn enables the measurement of mass flow.

The effectiveness of a DP flow transmitter for steam flow depends on the primary element used. Flow nozzles are well suited for steam flow because they can handle the high temperatures and pressures that accompany steam flows. Orifice plates are widely used to measure steam flow. In fact, all the primary elements, including Pitot tubes, Venturi tubes, and wedge elements can be used for steam flow measurement.

2. Vortex Flowmeters
Vortex flowmeters have some advantages over other types of new-technology flowmeters when it comes to measuring gas and steam flow. Gas flow measurement is still a relatively new application for Coriolis meters, and the use of Coriolis meters to measure steam flow is just beginning to occur. While ultrasonic meters have been used for a number of years to measure gas flow, steam flow is a very new application for them. Magnetic flowmeters cannot be used to measure either gas flow or steam flow. Multivariable differential-pressure flowmeters can be used to measure liquid, gas, and steam. However, most multivariable DP flowmeters have substantially greater pressure drop than vortex meters, due to the presence of a primary element.

Steam is the most difficult fluid to measure. This is due to the high pressure and high temperature of steam and because the measurement parameters vary with the type of steam. Main types of steam include wet steam, saturated steam, and superheated steam. Steam is often measured in process plants and for power generation. In addition to their ability to tolerate high process temperatures and pressures, vortex meters offer wide rangeability, which enables the measurement of steam flow at varying velocities. In process and power plants, steam is often measured coming from a boiler.

3. Variable-Area Flowmeters
Variable-area meters, also called rotameters, have a limited use for steam applications. One reason is that many of them do not have an output signal and must be manually read, although some companies have developed variable-area meters with an output signal. Most process and power plants today are highly automated and would find a flowmeter that has to be read manually of limited value.

Another reason for the limited use of variable-area flowmeters is that they have low accuracy. Many variable-area meters have accuracy levels in the +/-5 to +/-10 percent range, which is generally not suitable for measurements in process and power plants. If end-users want to go to a low-cost meter, they will be more likely to try a DP flowmeter than a variable-area meter.

Variable-area meters do have the advantage of being low cost though, so they are a good fit for noncritical measurements where high accuracy is not a requirement.

4. Target Flowmeters
While target flowmeters can be used for liquid, gas, and steam applications, they are predominantly used to measure steam flow. Target meters can measure both superheated and saturated steam. While the target is subject to wear, this can be compensated for with recalibration. The target meter has no moving parts, and it can withstand pressures up to 15,000 PSIG and temperatures up to 500 F. Target meters can fit into almost any line size above 3/8”.

Even though target meters were developed after 1950, they are classified as a traditional-technology flowmeter, due to their primarily mechanical means of construction. It is not obvious why more suppliers have not chosen to offer this meter, because, in many ways, the target meter is most like a vortex meter. Target meters rely on a body inserted into the flowstream, not unlike the bluff body that characterizes vortex meters. However, instead of counting vortices generated by the bluff body, like a vortex meter, a target meter measures the force exerted on the target by the fluid.

5. Turbine Flowmeters
Turbine flowmeters are widely used for liquid and gas applications, but they have very limited use for steam flow measurement. One major issue has to do with the effect of condensation on measurement accuracy. When condensation occurs in a flowing stream, the fluid becomes a mixture of steam and water, which creates two-phase flow. The condensate can harm the blades, and interfere with measurement accuracy.

Turbine flowmeters do have an advantage since they can perform better at low flowrates than vortex flowmeters. They also have a good turndown ratio (some suppliers claim a turndown of 25-to-1). The most favorable condition for steam flow measurement by turbine meters is measurement of dry steam. However, because steam is so readily influenced by changes in temperature and pressure, steam flow conditions can change very quickly. Steam is most stable at the boiler, but cold spots can occur in the line, bringing about condensation.

6. Coriolis Flowmeters
Coriolis flowmeters can be classified as an emerging technology for steam flow measurement. Like turbine meters, Coriolis meters have difficulty handling condensation in steam. When steam condenses, the water droplets create two-phase flow, a mixture of steam and water. The presence of water interferes with the accuracy of the flow measurement.

Coriolis flowmeters can work to measure flow with dry steam. However, because steam is easily affected by variations in temperature and pressure, steam-flow
conditions can change very quickly. There remain some technical challenges for Coriolis suppliers to resolve before Coriolis meters can be a major part of the solution for steam flow measurement.

7. Ultrasonic Flowmeters
Ultrasonic flowmeters have many advantages over both traditional and new-technology flowmeters. They are minimally invasive, have high accuracy, cause little-to-no pressure drop, and they have no moving parts. However, there are some technical limitations that make steam flow a difficult application for ultrasonic flowmeters.

One limitation of ultrasonic flowmeters applies to clamp-on flowmeters. The speed with which an ultrasonic wave travels through metal may be different than the speed of the wave through steam. This can interfere with the accurate calculation of the flowrate of the steam. In addition, the exact thickness of the pipe is not always known, either because there is buildup or deposits on the pipe wall or simply because this is an unknown variable. This pipe-thickness issue applies to all clamp-on flowmeters, whether they are measuring liquid, gas, or steam.

A limitation of spoolpiece ultrasonic flowmeters is that the transducers can become overheated due to the temperature of the steam. If this happens, it can ruin the transducers. While some ultrasonic flowmeter suppliers have found a way to successfully deal with this issue, it remains an important technical challenge.

Vortex Offers a Safety Net
Some suppliers of turbine, Coriolis, and ultrasonic technologies for steam flow measurement have added vortex meters to their product line so as to have an alternative technology to offer end-users who may have difficulty measuring steam with a given technology. The function that vortex meters have as a kind of back-up meter, or safety net, for companies offering difficult-to-apply technologies is likely to grow as end-users increase their willingness to try new technologies for measuring steam.

Vortex flowmeters are very reliable when used to measure steam flow, they cause minimal pressure drop, and they can handle high pressures and temperatures. The ability of vortex meters to measure steam flow will encourage suppliers of alternative technologies to further develop and promote their alternative technologies for steam flow measurement, knowing that they can always fall back on their vortex meters for difficult applications.

So choose your meter carefully. You can share your experience for the benefit of all in this area..based on the reasons you selected the particular type of flow meter.

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December 17, 2008

Quick Tips for Saving in Pumps

If you want to get some quick energy saving tips follow these guidelines to identfiy opportunities in CW pumping, Or may be in all pumps with slight care.

This is the method which also guarantee you minimum energy saving achievable in pumps. The actual savings will be higher always depending on various other factors. I used this method recently & saved ~15% power consumption in CW pumps i.e. ~600 kW out of 4000 kW load resulting in huge savings with a payback of merely 4 months.


Guidelines
  • First of all make a list of all pumps with design flow & head in two different columns in an Excel sheet. Say column A with flow & Column B with head

  • Now measure the power consumption in the field & put it in Column C.

  • Now in Column D put calculated power consumption with efficiency available for new pump & high efficiency motors.

  • New pump efficiency for CW flow of more than 300 M3/hr at 40 m head can be considered ~80% which can go as high as 85% for bigger size pumps beyond 1000 M3/hr.

  • High efficiency motor can have efficiency in the range of 94%+for motors of >100 kW, which can be 96%+ for bigger motors >300 kW

  • After getting the final figure of power consumption for a new pump, you can put the saving potential in the next column E.

  • Put the investment required for motor & pump in next column F judiciously (you can ask me for indian cost roughly) Or get it from some vendor

  • Put payback or ROI in the next column G


You are through now. Suggest the replacement to your management in a nice presentable format for approval. Mind it that this method gives you minimum guaranteed savings from these pumps because,

  • This method is not considering any flow & head measurement therefore, you get minimum savings in case your pump is not delivering the design or considered flow. Anyway it can not deliver more than design without compromising on head.

  • The chances of errors are very less as you are measuring only power which is measured reliably & more accurately.

  • You do not have to deal with plant people convincing them about the accuracy of flow measurement. Because flow is the most troublesome area where mostly people do not believe (Or they dont want to) about large drops.

  • This gives you option of selecting the latest & most efficient equipment in the market.


Don't you believe on this?

I Said......I have already saved 15% power i.e. ~600 kW.

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December 10, 2008

Equal Percentage Valves - Opening Vs Flow

In case of equal percentage valves, the flow varies according to the following definition.

'Any % change in the opening from its current existing value changes the flow by same percentage of its current value at current opening.'

Means if current opening is say 10% & u change it to 15% than the change in opening from its current value (of 10%) is 50%, so the flow will also increase by 50% of its existing value at 10% opening. This means if flow was say 20% of the total range (Or capacity of the valve) at 10% opening it will become 30% (50% higher compared to 20%) of the total range.

So how to calculate it????

Now you know the definition so you can generate an equation which gives you all the values where 0% opening or lift is 0% flow while 100% lift is 100% flow.

So the curve for these valves look like this.




Long back I generated an equation from a general curve for an equal percentage valve. Its fixed for all kinds of valves from any manufacturer generally. There may be minor variations in case of specially designed valves otherwise it is same.

The equation is.

% Flow is = .06 + 0.49 * X -.019 * X^2 +.0005 * X^3 - 0.0000502 * X^4 + 0.0000000242 * X^5

Where X is % Lift or opening , X = 60 for 60% opening & not 0.6

Hope it is useful for all.

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December 04, 2008

Pinch Technology: Some Basics


Most Industrial processes involve heat transfer from one process stream to another process stream (interchanging) or from a utility stream to a process stream. In the present energy crisis scenario, target in any industrial process is MER – Maximum Energy Recovery or Minimum Energy Requirements.



In the early days of pinch technology, the main emphasis was on heat exchanger network (HEN) design. Today pinch technology stretches far wider in the fields of overall process improvement and utility system design

Pinch Technology analyses process utilities (particularly energy and water) to find optimum way to use them, resulting in financial savings. It does this by making an inventory of all producers and consumers of these utilities and then systematically designing an optimal scheme of utility exchange between them. Energy and water re-use are at the heart of pinch technology.

With the application of pinch technology, both capital investment and operating cost can be reduced. Emissions can be minimized and throughput maximized.

What is Pinch Technology?
The term “Pinch Technology” was introduced by Linhoff and Vredeveld to represent a new set of thermodynamically based methods that guarantee minimum energy levels in design of heat exchanger networks. It also ensures minimizing the capital costs and fewer emissions.

Basis of Pinch Analysis

Pinch Technology represents a simple methodology for systematically analyzing chemical processes and the surrounding utility systems with the help of the First and the Second Law of Thermodynamics.

1st Law of Thermodynamics: Provides the energy equation for calculating the enthalpy changes (ΔH) in the streams passing through a heat exchanger.

2nd Law of Thermodynamics: Determines the direction of heat flow. That is, the heat energy may only flow in the direction of hot to cold. This prohibits ‘temperature crossovers’ of the hot and cold stream profiles through the exchanger unit.

In practice the hot stream can only be cooled to a temperature defined by the ‘temperature approach’ of the heat exchanger. The temperature approach is the minimum allowable temperature difference (ΔTmin) in the stream temperature profiles, for the heat exchanger unit. The temperature level at which ΔTmin is observed in the process is referred to as the “pinch point” or “pinch condition”. The pinch defines the minimum driving force allowed in the exchanger unit. Thus, the prime objective of pinch analysis is to achieve financial savings by better process heat integration (maximizing process-to-process heat recovery and reducing the external utility loads).



Pinch principle

The point where ΔTmin occurs is known as the “Pinch”. Once the pinch has been identified, it is possible to consider the process as two separate systems: one above and one below the pinch as shown in the figure.
The system above the pinch requires a heat input and is therefore a net heat sink. Below the pinch, the system rejects heat and so is a net heat source



To summarize, the understanding of the pinch gives three rules that must be obeyed in order to achieve the minimum energy targets for a process:

  • Heat must not be transferred across the pinch, i.e., no temperature crossovers.
  • There must be no external cooling above the pinch.
  • There must be no external heating below the pinch.


JUST FOR FUN & General Knowledge
After so much of pinch technology I would like to mention a few more pinches here :)
Ever heard about Network Pinch, Hydrogen Pinch, Water Pinch or Z Pinch?

NETWORK PINCH:When optimizing energy consumption in an existing industrial process, a number of practical constraints must be recognized. Traditional Pinch Technology focuses on new network designs. Network Pinch addresses the additional constraints in problems associated with existing facilities.

HYDROGEN PINCH:The Pinch Technology approach applied to Hydrogen management is called Hydrogen Pinch. Hydrogen pinch enables a designer to set target for the minimum hydrogen plant production and/or imports without the need for any process design.

WATER PINCH:This is a systematic technique for analyzing water networks and reducing water costs for processes. It uses advanced algorithms to identify and optimize the best water reuse, regeneration, and effluent treatment opportunities. It has also helped to reduce losses of both feedstock and valuable products in effluent streams.

Z PINCH:In fusion power research, the Z-pinch, or zeta pinch is a type of plasma confinement system that uses an electric current in the plasma to generate a magnetic field that compresses it (Pinch). The name refers to the direction of the earliest experimental devices in England, where the current flowed down a vertical quartz tube, the Z-axis on a normal mathematical diagram.

By Associate Writer - Nidhi Garg

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