Boiler Efficiency - Parameters affecting it

Energy savings does not always imply efficiency improvement in boilers therefore, we need to understand the factors which are affecting it. So basically one should know all those parameters that influence efficiency.

For this one should know how to calculate the energy savings from parameters that do not influence thermal efficiency.

For very clear understanding between an increase in steam generation and improvement in efficiency, I have always emphasized that process engineer should be very clear about his options, definitions, & actual process happening due to modification proposed in the name of energy efficiency.

Recall the general efficiency equation of a boiler

(1) Eff = Absorbed Heat / Energy Input

The equation says nothing about the fact that not all adsorbed heat is useful heat. For instance the blow down is certainly “adsorbed” heat but rarely “useful”. In other words the energy in the blow down will be lost to ambient but any change in the blow down rate will not affect the system efficiency.

Equation (1) was converted into another equation


(2) Eff = 1 - Losses / Energy Input


It was shown that equation (1) and equation (2) are equal and should give the same result.

The energy input to the system is in the most simple case the energy of the fuel and the enthalpy of the combustion air. However one may add to the ener0gy input the steam necessary to atomize the fuel, or the electricity needed to power all electric motors of the boiler. In large power plant boilers it is especially important to draw a system boundary and prepare a list of all energy flows that enter and leave the system boundary.

Similarly the sum of losses depends on what we call a loss. Some obvious losses are the energy in the stack gas, the radiation and convection loss, and the refuse loss. However blow down is not considered a loss and therefore excluded from the sum. In fact the norms state no blow down is allowed during efficiency testing.

Using the efficiency simulator one will notice that system efficiency does not change at all if the following parameters are changed

• The steam pressure
• The steam temperature
• The blow down fraction
• The percentage of condensate return
• The condensate return temperature

The above parameters do not enter equation (2) and consequently the system efficiency will not change.

Nevertheless lowering the steam pressure or temperature or increasing the condensate return and temperature will certainly save fuel. There is absolutely nothing wrong with the definition of efficiency except the fact that we may save fuel by not changing the system efficiency at all.

Whenever Ps , Ts, xBD, xcon,Tcon, change the steam output changes as well, but the efficiency stays the same. Consequently we cannot calculate the fuel savings by the equation

(3) Fuel Saving % = ( Eff new - Eff old ) / Eff new


Another peculiarity are the savings one may achieve by preheating the air or the feedwater. The efficiency definition does not provide for entering the temperature of preheated air or feedwater, because preheating devices such as an economizer and air preheater are inside the system boundary. In other words preheating of the combustion air and the feedwater is taken into account through lowering the stack gas temperature.

So basically, the major purpose of writing it to again clarify that fuel saving does not necessarily mean the increase in efficiency. Currently I have worked an oil water emulsion technique which makes nano particle mix of fuel saving 3-5% fuel but there is no change in the efficiency of the system as none of the boiler parameter is changing. This makes saving just by using water as fuel.

So be Careful.


This Article is reproduced from the paper of GTZ from BEE India website.

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CIP Filters: Popular Types

In the first part of selection criteria of CIP filters, we have discussed about the cost factors while in the second part of it we have mentioned about some important benefits. In this post I am sharing few types of CIP filter which may be useful for all process engineers.

This is a very short post with few details on various common & popular type of CIP filters.

In this category of filters that is CIP (or Cleaning in Place), the following are the major type of elements.

1. Candle Filters
CIP polish filters for fine filtration up to 1 micron with the help of precoat or body feed. this type of filters are ideally suited for carbon removal or catalyst recovery type of application where very fine particles are involved and if you use any other media it may clog easily.

It protects operator from hazardous handling and pyrophoric solids if involved.

2. Auto Self Cleaning Filter
For filtration of cheaper fluids like water at high flow rates and filtration requirement of 50 micron and more, this is the best CIP filter. It can be used for process fluid also, waste water treatment, utilities etc. Cleaning is generally done by the same filtrate to avoid any effluent generation even in the chemical processes.

3. Auto Cleaning with Scrapper
Now new technologies are coming up day by day for all process operations. For various viscous liquids like sugar, oil etc the filtration is always very tough and is the biggest cost consuming item. Now technologies are available for such operations e.g. scraper mechanism for cleaning of filter surface.

In the above sketch you will realize that top left of drawing is having a baffle shape plate which is a scrapper and rotates continuously at slow speed. This helps in removing the choking and continuous removal of solids.

4. V Sep Filters
V sep filters are used in very large scale handling like sewage treatment plants, coal washeries, Municipal waste and CETPs where large scale general operation of main bulk separation is required.

5. Basket / Strainers
Last but most used category is the filters used for pumps which are more commonly known as basket filters or strainers. They may be in different shapes & sizes and will be in many different options.

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CIP Filters: Selection Criteria - 2

In the first post on CIP, we have listed few options which are essential to be evaluated for the economic and beneficial selection of CIP filters compared to conventional type.

I hope it was good and easy to understand for all those who are looking for useful information on filters.

In this part, I am putting some facts related to payback or economics understanding for replacement decision and I will also cover various other factors apart form major cost items which works out in favor of CIP.

After deciding to go for CIP type filters as per criteria in first part of this post, please look for following parameters which can justify your decision based on cost payback. They are.

1. Capital cost of proposed new filtration system.
2. Filter element life & cost of spare elements.
3. Manpower reduction or increase and cost impact of it.
4. Product loss - Saving or Increase.
5. Space requirement - Saving or increase
6. Capacity of the system.
7. Downtime and production loss.
8. Energy cost including all aspects as described in Part-1 of this post.
9. Cost of cleaning system.
10. Cost of disposal.
11. Change in Cost of Consumables
12. Other cost factors if any.

It is always recommended to make a tabular comparison with comprehensive study as it is not very easy to decide about the replacement of any filtration system because it is the toughest unit operation and further you need of lot of re-search work on trying new system's suitability for your fluid, for your process. So be careful and give appropriate weight to each important factor without any preoccupied decision.

Generation of waste and associated management cost factors are very high now in any chemical plant so be careful that all such cost factors are included in your evaluation.

Now to achieve the reduction in such cost factors like waste management etc. CIP is the first switch from disposable media such as cartridge or bag filters. the initial cost of such disposable filters is less and therefore, they are the first choice in general but in the long run if we analyse the life cycle cost including all cost factors as indicated in the first post, the CIP filters are more advantageous.

Following are the major factors which can lead to significant improvement.

1. No Waste Disposal
With cleanable filters, there are no spent cartridges, or bags for landfill or to incinerate. This saves lot of cost on waste disposal in terms of used bags / filter elements. In case of cleanable filters, you need to dispose only solids and wash liquid which can be re-used to reduce the overall load on ETP.

2. Cleaning frequency Vs change out frequency
Generally disposable media is discarded at fix frequency which is usually higher than required to safeguard the production and to maintain uninterrupted operation. On the other hand cleaning generates less effluent due to precise requirement whenever it is indicated based on differential pressure. This avoids unnecessary load on ETP by doing the cleaning activity at right time. So overall cost is less.

3. Reuse of Waste
In general, the cleaning fluid is compatible with the process so in most of the cases it can be recycled back to the process system without any effluent load. Even if it is very diluted washing it can be recycled in the next cleaning operation and thus reduction in overall effluent load can be achieved.

4. Loss of Product
Generally if you are using disposable media, mostly the process liquid or solid are lost with it and that is a direct loss of yield. This is mainly due to drainage of dead volumes, opening of seals etc.

5. Environment
As explained in the first post, many possibilities of spillage, exposure of workers, landfill liabilities etc etc are associated with disposable system where frequent opening of the entire system is required specially in pharma & food industry.

Apart from above direct benefits many indirect cost items are always there in proportion to the manual activities. So naturally those costs are very high for disposable media compared to CIP filters.

In next article I will try to describe few CIP filter in a short post.

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CIP Filters: Selection Criteria - 1

Hi Friends, I am really sorry for coming back so late this time. It was really a very tough experience of life for me in last 2 years as I lost my job, struggled a lot, regaining it now in 3 steps. Very tough….Very Very tough to survive. But good also as it gave me a clear picture of about real friends and those who pretend to be your friend but actually are not even a human being…….Anyway. 

 I am now starting the topics on tougher issue of process engineering i.e. Filtration. It’s not in a sequence as I am not in a position to find my papers one by one during this turmoil. So this one is related to selection criteria of CIP filters. How to choose them and what are the factors affecting selection. 

The concept of CIP dates back to 1950 when it was first developed & applied in Dairy Industry. 

The conventional definition of CIP (Cleaning In Place) as name suggest is the removal of process contamination and cleaning of process system by re-circulation or spray application of flush, wash & rinse solution without removal or dismantling of process equipment’s. 

Now first let us understand the factors important for CIP filters.

1. Clarity of Filtrate 
This decides the no of stage required in a filtration system. The higher the no of stage of filtration, higher will be the filtrate clarity. More the no of stages, it is difficult to handle the filtration process / system in terms of maintenance etc. Hence, it’s better to use CIP filters to reduce various cost components as given below. 

2. Cost of Operation 
What are the factors contributing towards cost of filtration? Other than indirect cost factors some direct cost components are more important to work out for the overall cost of filtration. These factors are 

a. Cost of Filter Element 
In general, the costs of operation are generally lesser in case of cleanable filter elements as compared to single use type or use & throw type. This is simply because of higher material processing output in the same cost. The disadvantage of using a single use type element is mainly the disposal cost and safety aspects. 

b. Cost of filtration aid (if applicable) 
Lot of lab work is required to find out suitable aid before going into commercial operation. Then optimization of its quantity is required and then cost optimization is required. 

c. Energy Cost 
The cost of energy to operate the feed system, pumps, filter itself, cleaning system etc. etc. is to be calculated. The point is that it is not only main filtration system but all the paraphernalia is to be included in energy cost. 

d. Cleaning System The cost of cleaning the entire filtration system includes, the downtime cost, the consumption of cleaning media, the power consumption during cleaning and re-assembly. The re-charging of the entire system, the losses, the time consumed in making pre-filtration bed etc. is a cost of operation of selected filters. 

e. Manpower
Generally, during main operation cost of manpower is less as today we have many automatic systems in all types of filtration's but the major manpower cost comes during cleaning where time is an important factor and hence excess manpower is required. Generally this manpower is than adjusted in some other jobs as compromise. 

f. Loss of Product 
Every time the filter is stopped for any activity like cleaning etc. there is some spillage loss, some loss due to dead volumes in the vessels filter etc., some losses in the form of liquid content of solids, pipeline drainage etc. All these factors contribute to a significant yield loss of product in general. Here the concept of CIP is very useful in such scenarios. 

3. Filter Size 
In general, if frequent cleaning requirements are there batch cycle time (unproductive) goes high and to compensate for that process engineer will select larger size of filter. This increases space requirement, cost of structure to hold it, higher capital cost. This also means high downtime and high production loss in case of failures. So again CIP is better. 

4. Safety 
Safety of operator is most important part of any chemical process so is the case with filtration as well especially when material is hazardous or toxic in nature. The importance of a closed system is of utmost priority due to such nature of process fluid. The minimum operation in manual mode e.g. opening and cleaning of filtration system is never permitted and CIP is the best solution in such cases. 

5. Environment 
This is another neglected aspect which is now in focus in all chemical industries. Whether it is CIP or no CIP it has to use lesser amount of cleaning fluid to generate less effluent. This is also the reason of avoiding use & throws filters as they pose serious threat to environment if disposal is not safe & not regulated. In EU countries, due to strict norms of disposal, the cost of disposal of used filter element is higher than new one and that is right in a sense that if we do not care for our environment one day it will be full of waste. So we have to regulate it. 

Above issues and factors are to be considered during a new selection of filter type and are more prominent if we are planning for replacement study. In general, if safety & environment is the major concern OR material is toxic or hazardous it is simple to decide to go for CIP filters. Once decided, plan for the replacement of old filters quickly. For the economic evaluation / justification criteria for the management shall be given in my next post CIP – Filter Selection Criteria – 2.

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