Avtomatisation of industrial coal burning boiler

[justawnb]

Homework Statement

Image: http://www.coal2nuclear.com/Fossil%20Fuel%20Power%20Station%20Core%20-%20Relabeled%20-%20982.jpg

I need to know the critical parameters of getting steam, so that i know which measuring instruments to use and where to put them so that following statemnts are true.

- temperature of steam must be as constant as posible
- operation of the boiler must be energy efficient
- operation of the boiler must ensure reduced to a minimum abrasion of parts of boiler
- operation of the boiler must comply with the legal requirments of purity of gas emissions.

So i have been reading a lot of stuff about it, but i just don't totaly get it.
I would appreciate if someone can give any good link on this, where the actual process on the image above is explained in a litle more detail, since i found and read a lot of articles and i just don't know enough to solve this problem.

ty all

 

[CWatters]

This isn't a process that I'm an expert on but.. ..

Looking at the diagram you can see the burner in the boiler. Follow the path from the flames around to the left where it says "to stack". The exhaust stack isn't actually shown but would be off page to the left. As the exhaust gasses go along that path they get cooler but still contain useful energy. So there are three coils and a Heat Recovery unit that extract energy of different quality in this path. From best/hottest to worst/coldest you have "Superheat", "Reheat", "Preheat" and "Heat Recovery". Forget the names for the moment. Just think of them as outputs from the boiler that extract different grades of energy. The idea being that the exhaust stack temperature should contain as little waste energy as possible.

Each of these four boiler outputs is used for a different purpose. The hotest "Superheat" output is used to drive the main "hi pressure" turbine. The "Reheat" output is used to drive the "int press" (Intermediate Pressure) turbine. The "preheat" output is just used to preheat the water for the Superheat and Reheat circuits. The Heat Recovery output appears to be heating the coal dust before it goes into the burner.

Then on the right.. The output of the Intermediate Pressure turbine still contains useful energy so it's fed to a low pressure turbine. The output from that contains little useful energy but it's still steam and is converted back to water in a condenser. Even after condensing the water is still hot so it's fed back to the boiler rather than using fresh cold water. Some energy is wasted up the cooling towerd. In some countries I believe they pipe it to a nearby green house and use it to grow toms.

In short.. As much energy as possible is extracted from the flames/exhaust gas AND as much energy as possible is extracted from the resulting steam.

 

[CWatters]

As to where to put sensors, I'll let you work out what you might want to monitor.

The tricky one is the question about abrasion. Google suggests it's a problem for bends in the coal dust path. I can't see how you can control the boiler to minimise that. What I mean is the speed of the dust is dictated by the power required so it's not something you can adjust to reduce wear without reducing power. Perhaps abrasion also occurs in the boiler if not all the coal dust is burnt? Not sure how to monitor that - perhaps they look at the exhaust gas and check it's C02 not C0?