I have a designed boiler producing 100K LB/HR steam @150psig. Now I would like to have 300psig steam with same capacity. Does the higher pressure affect the boiler design? I knew it will change the thickness of steam drum and all the steam piping. What I want to know is if it will change the size of steam drum, boiler capacity, firing rate or water level control, etc? if I assume using same heating surface and fuel. Thanks for your advice.
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Steam pressure vs. boiler capacity 1
- Thread starter ZHWIL28
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What is your fuel and firing system? A lot of times we have customers who try to squeeze more out of their system then design and they end up flooding the chamber which hurts their combustion. But that does not mean that it is impossible to get more out than design.
To increase your output you are going to have to increase your temperature or fuel feed rate. Your system may or may not be designed to handle the increase in the fuel feed.
Other things to consider....What emission controls do you have? Burning more fuel will produce more exhaust gases so you could have a bigger pressure drop accross any emission controls, boiler, ducting, etc. If you have an ID fan it may not be able to maintain the necessary draft.
Also, if your temperatures goes up you could start getting problems with overheating your chamber causing ash problems. Or you may exceed temperatures limits on any other components in the system causing them to fail.
There may be other factors to consider depending on your fuel and firing system.
To increase your output you are going to have to increase your temperature or fuel feed rate. Your system may or may not be designed to handle the increase in the fuel feed.
Other things to consider....What emission controls do you have? Burning more fuel will produce more exhaust gases so you could have a bigger pressure drop accross any emission controls, boiler, ducting, etc. If you have an ID fan it may not be able to maintain the necessary draft.
Also, if your temperatures goes up you could start getting problems with overheating your chamber causing ash problems. Or you may exceed temperatures limits on any other components in the system causing them to fail.
There may be other factors to consider depending on your fuel and firing system.
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The fuel is wood waste and there is a supplemental dust burner. Thanks,you are right. Increasing fuel feed surely will change a lot as you mentioned, even heating surface I am worried, since the heat flux may be too high. However, at this moment I want to know if the change of steam pressure only will change boiler significantly and what the major changes are? Thanks for input agian.
Before we waste time dreaming about what might or might not have to be done with various components of the boiler, the question has to be answered if the metal components (pressure parts) are rated for 300PSIG. If the boiler has enough metal in it to meet the 300PSIG rating and can be recertified for that pressure (if necessary) then the rest of it merits investigation. If not....moot point.
rmw
rmw
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It depends on how sophisticated the boiler mfr is. Several things would change , besides the wall thickness of pressure parts, including:
a) the steam outlet enthalpy changes, so the boiler firing rate must change. This affects fan size , burner size, emmissions permits, etc.
b)The sizing of the steanm drum driers and seperators may need to change, based on the changed specific volume of steam ( driers) and 2-phase flow (seperators). For large natural circulation boilers, the drum sizing is usually dictated by the length and dia. needed to contain these driers and seperators.
c)To prevent dryout and DNB in the waterwall tubes, the waterwall circulation system is designed to ensure an adequate circulation ratio is provided. This involves the sizing of the downcomers, inlet feeders, inlet headers, watewall tube size, outlet header and unheated outlet risers, the distribution of these risers to sections of seperators and segmenting of headers. This calculation is dependent on the specific volume of steam, as well as the distribution of radiant heat absorption in the furnace. The higher pressrue leads to a smaller steam specific volume and a reduced driving force for natural circulation.
d) Above certain pressures, there is usually mandated a change to the range of permitted feedwater treatment methods and water quality, espescially if the boiler is feeding a steam turbine.
a) the steam outlet enthalpy changes, so the boiler firing rate must change. This affects fan size , burner size, emmissions permits, etc.
b)The sizing of the steanm drum driers and seperators may need to change, based on the changed specific volume of steam ( driers) and 2-phase flow (seperators). For large natural circulation boilers, the drum sizing is usually dictated by the length and dia. needed to contain these driers and seperators.
c)To prevent dryout and DNB in the waterwall tubes, the waterwall circulation system is designed to ensure an adequate circulation ratio is provided. This involves the sizing of the downcomers, inlet feeders, inlet headers, watewall tube size, outlet header and unheated outlet risers, the distribution of these risers to sections of seperators and segmenting of headers. This calculation is dependent on the specific volume of steam, as well as the distribution of radiant heat absorption in the furnace. The higher pressrue leads to a smaller steam specific volume and a reduced driving force for natural circulation.
d) Above certain pressures, there is usually mandated a change to the range of permitted feedwater treatment methods and water quality, espescially if the boiler is feeding a steam turbine.
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Thanks for all your inputs. Sure, all pressure parts have to be checked. Fortunately, I am just checking the changes for a similar boiler design not retrofitting a existing boiler.
Regarding to davefitz's comments:
1)The saturation enthalpy changes from 1195.6 Btu/lb to 1203.2 Btu/lb, so the change of output is relatively small.
2)The steam volume reduces as a result of higher pressure, so the internal parts likely are smaller.
3)Now I think the problem may lie in the circulation. To keep the circulation rate, I have to either increasing firing rate which will increase gravity difference between downcomers and risers or changing the heating surface which I would like to avoid. The higher firing rate may induce the overheating problems which require to evaluate the flow in the tube. Does anyone have an idea how large the effects will be?
Thanks
Regarding to davefitz's comments:
1)The saturation enthalpy changes from 1195.6 Btu/lb to 1203.2 Btu/lb, so the change of output is relatively small.
2)The steam volume reduces as a result of higher pressure, so the internal parts likely are smaller.
3)Now I think the problem may lie in the circulation. To keep the circulation rate, I have to either increasing firing rate which will increase gravity difference between downcomers and risers or changing the heating surface which I would like to avoid. The higher firing rate may induce the overheating problems which require to evaluate the flow in the tube. Does anyone have an idea how large the effects will be?
Thanks
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