Question About Water Tube Boilers 3

[ChemicalAg]

Hello,

I am a recent graduate and I just started my first job at a specialty chemical plant. One of my 1st assignments is to monitor our natural gas consumption.

In order to calculate the efficiency of a boiler it is simply the Steam Energy Produced/Natural Gas Energy Consumed correct?

Well I was able to collect the data that I need from our natural gas supplier for the energy consumption. However, this plant is only 1 year old and there is not enough instrumentation to collect the data that I need for the amount of steam produced.

My questions are the following:

1.) What steps should I take in order to get an accurate estimate of the amount of steam produced?

2.) Once I calculate the correct boiler efficiency, what calculations do I need to make as far as air flow rate?

Thank you

 

[gpbche]

ChemicalAg,

1. If you do not have a steam flow meter on the boiler output I would install one with a totalizer. I do not know of a way to accurately estimate steam production. Steam demand can very significantly in the course of a day. Vortex or orifice meters are fairly inexpensive.

There are other factors that can effect efficiency like boiler feedwater temperature, percent of condensate recovered, economizer performance, etc.

I recommend checking the DOE Industrial Technologies Program for steam best practices.

http://www1.eere.energy.gov/industry/bestpractices/steam.html

The attached .pdf has a way to benchmark the cost of steam production.

Good luck.

 

[rmw]

Do you measure your boiler feedwater flow anywhere?

rmw

 

[davefitz]

The usual means of calculating efficiency requires the accurate measurement of only one flow. Normally that flow is the feedwater flow. But if your site only has accurate measurement of the fuel gas flow, then you could modify the procedure to use that flow as the ultimate indicator of unit load.

Other data that would be needed is feedwater inlet temperature , drum pressure, blowdown flowrate ( or isolate it for the test), steam outlet pressure and temperature, and stack O2 and/or CO2 level, inlet air temp ,and stack exhaust temp.

refer to the asme power test code PTC 4 or summary description in the B&W Steam book.

 

[aimeem]

Hi RMW,
i also have the same problem. I have the data for boiler feedwater. How should i proceed?

THanks!

 

[rmw]

Either of the two referemces mentioned by davefitz will work. Your water flow in is an indicator of the steam flow out and with that information and what you know about the steam and flue gas out you can do the calculations. Be sure to account for any boiler blowdown as that does not become 'steam out', but it is "BTU's out".

rmw

 

[Drexl]

Hi,

For a full calculation using different methods, see EN 12952-15 Water-tube boilers and auxiliary installations. Acceptance tests

br
Drex