Sr. Manager (Steam Engineering Applications)

Coimbatore


Schematic diagaram of water wall membrane boiler



G.A. of External Furnace


 


In the last few years, in authors experience he has been observing that by and large the textile processing industries have gone for water wall membrane boiler even boiler capacity like 3 TPH and 4 TPH considering that they would use multi fuel incase of shortage of fuel like wood.


But in reality invariably customers have been using only wood no other fuel has been tried out even though fuel like biomass available with high calorific value.


In authors experience, if the steam demand requirement is up to 4 TPH, customers can very well use packaged boiler because of the following reasons:


  • Space requirement is 1/3rd of water wall membrane boiler
  • No need to use FD Fan if there is no air pre heater
  • Boiler water TDS can be maintained up to 3500 ppm
  • Simple soft water is more than sufficient to run the boiler
  • Easy to maintain the boiler as it is very easy to clean tubes
  • There is no RCC structure required to position the shell
  • Observing water level in the shell is more convenient than WWMB
  • In case of gas conversion, conversion is so easy and the conversion cost is only 25 % of boiler cost and boiler efficiency can be maximum of 85 %.
  • Maximum boiler efficiency can be of 77 % with Heat Recovery system on wood.
  • Only one blow down valve so easy to operate
  • Leading and positioning of boiler is very easy with minimum cost.
  • Refractory work is very minimum and maintenance of refractory and replacement cost is very minimum.
  • Erection cost is very less.


Limitations of packaged boiler:


This boiler can be given up to 4 TPH at 10.5 and 17.5 Kg/cm2.


When to choose water wall membrane boiler?


  • It is best option if the fuel is powder fuel like Baggasse, Husk, DOB, coal because volatile matter is more in powder fuel than wood and it requires more volume to complete the combustion.


  • It is very ideal boiler if the load is constant load because steam fuel ratio can be achieved at 1: 4 if the boiler is operating at 100 % load. In case boiler operates at lesser load i.e. 50 % of the load then the steam fuel ratio drastically gets reduced to 1: 2 because of reasons like more heating surfaces, radiation loss, frequent opening and closing of fire door etc. In case of packaged boiler, there is a slight increase in steam fuel ratio at lesser load while compare to WWMB.


  • If the steam requirement is 6 TPH or 8 TPH or 10 TPH, customers can very well to opt this design based on the peak load condition in the process.


What are the other ways out to increase the steam fuel ratio?


In authors experience, if the peak steam requirement is only momentary let us say 30 minutes to 60 minutes then it is advisable to use boiler load management system with two numbers of packaged boiler instead of one big capacity of water wall membrane boiler.


Example:


Boiler running at without boiler load management system:


Steam load Boiler 1 SF @ Blr 1 Boiler 2 SF at Blr 2 Avg Sf

Kg/hr

6000 3000 kg 2.5 3000 2.5 2.5

4000 3000 kg 3.0 1000 2.2 2.75

5000 2500 kg 2.5 2500 2.5 2.5


 

Boiler running with Boiler load management system


Steam load Boiler 1 SF @ Blr 1 Boiler 2 SF at Blr 2 Avg Sf

Kg/hr


6000 kg 6000 4 - - 4

4000 kg 4000 4 - - 4

5000 kg 4000 3.5 1000 2 2.75



Difference in Steam fuel ratio with BLM



Steam load Boiler 1 Boiler 2 Diff in SF


6000 kg 4 2.50 1.5

4000 kg 4 2.75 1.25

5000 kg 3.5 2.50 1.00


If we consider the steam fuel difference for 6000 kg steam load with steam fuel ratio difference of 1.5 kg then the over all steam loss is as below:


Let us consider the fuel consumption per hour for 6 tph boiler is 1400 kg/hr and 20 hrs per day and 300 days running in a year.


Total fuel consumption per year: 1400 x 20 x 300


: 8400000 kgs


1.5 kg Steam lost because of boiler running at lesser load:


: 8400000 x 1.5

: 12600000 kgs of steam per year.

Assume that steam cost per kg is 80 paise including labour, power and wood.


The total monetary loss per annum is Rs.1 crore! It is really an eye opener to all the boiler users.


How to achieve maximum Steam fuel ratio:


Boiler load management system senses the steam demand in the process, based on the demand, boiler 1 runs at full capacity and it delivers the right quantity and pressure to the process.


Incase the boiler 1 pressure drops, it means that there is a sudden increase in demand in the process and hence, the second boiler which is in warm condition needs to be activated and steam will be taken from the boiler 2 automatically by control valve action and parallely the id fan also will be activated and pressure start builds up and boiler operator can charge fuel only at that time and need not to keep charging fuel all the time.


Conclusion:


It is suggested that all textile process houses are being advised that boiler must be ensure that it is running at maximum load with right selection of boiler model and capacity than choosing boiler based on the close knitted groups.



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