steam pressure reducing from 180psi to 80psi
steam pressure reducing from 180psi to 80psi
(OP)
At our plant we use our boiler as a heat transfering energy. my problem is we max out our boiler when we have a full load and i have an idea of fixing it if it works. we used to go to 150psi on our boiler which heated our railcars fairly well over a 24 hour period but we decided to try new things to reduce the coast of natural gas its been out of the roof! so we went to 85 psi on our boiler our railcars dont heat as fast but our gas usage has been great! my idea is if we crank our boiler up to 180psi and use a steam pressure reducer to 80psi. our boiler will easily put out 80psi without using alot of fuel and keep its pressure at 180 saving gas and still having our temp in the steam correct? basicly creating a super heated steam. so will we save money and heat our railcars faster? or will this back fire?





RE: steam pressure reducing from 180psi to 80psi
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RE: steam pressure reducing from 180psi to 80psi
RE: steam pressure reducing from 180psi to 80psi
I don't know if you'll get the benefits you're thinking of. No matter where you set your boiler, you're typically going to be generating saturated steam for your plant if you don't have a superheater in the loop. When you take the pressure from 180 psig to 85 psig in the boiler, you definitely will see a big decrease in your fuel reduction due to the massive reduction in the amount of energy you're pumping into the steam.
However, if you generate at 180 psig and then use a regulator to take the pressure down, you have to remember that for the system to be steady, every pound of steam coming out of the system after the regulator has to be accounted for by adding one pound of feedwater to replace it, which the boiler will heat up until it is 180 psig steam. That one pound leaving at 85 psig should have almost the same amount of energy in it (minus the losses due to inefficiencies in the system) that the 180 psig steam generated by the boiler has. In short, I believe you're going to get 85 psig superheated steam out of the system and the boiler will take just as much fuel to run because it's still generating 180 psig steam for use.
RE: steam pressure reducing from 180psi to 80psi
The boiler doesn't care what you do to the steam after it leaves. It just delivers the required mass flowrate of steam at the pressure it's set at.
RE: steam pressure reducing from 180psi to 80psi
RE: steam pressure reducing from 180psi to 80psi
<begin rambling. This is not meant to be serious.>
Sure, steam with more energy in it will generally be able to heat quicker than steam with less energy, but to heat the rail car from point A to point B always takes the same amount of energy, so the fuel costs should be the same. However, you have inefficiencies in the system that change according to the setpoints of the system. You also have throughput of the railcars to worry about... and so on and so forth.
<end rambling>
You can see how you might be in the situation where you can end up mired in questions, equations, and theory when one inexpensive test is really all you need if you can do it SAFELY (remember, steam holds HUGE amounts of energy and if it gets half a chance, it'll happily maim or kill). Could you take the opportunity to test each of your different operating conditions and generate datasets for each condition? Then, you can chart energy usage and productivity so you can compare how your plant reacts to the different conditions to pick the best.
With this problem, we can sit here all day and talk about the theory, but I think you've just got so much going on trying to modify an existing plant that spending a few weeks performing a conclusive test is going to be much better than trying to pin down all the places where the system will deviate from theory.
RE: steam pressure reducing from 180psi to 80psi
RE: steam pressure reducing from 180psi to 80psi
It also depends on what happens to the condensate your generating once you pass the steam into the rail car heating system- is it held at the same pressure as the supply steam and returned to the boiler? or blown down to atmospheric pressure?
RE: steam pressure reducing from 180psi to 80psi
I think you would need to study the railcar heating process and aim at minimzing the amount of heat lost from that process, perhaps there is a steam vent leak to atmosphere.
RE: steam pressure reducing from 180psi to 80psi
impossible and this process is a dead end. we cant do a whole lot more on the railcars persay, so im looking into other options.
and when the steam passes through the railcars it hits a thermal dynamic steam trap and dumps into our condensate line to a satalite tank than goes to our main condinsate tank. which both condinsate tanks are opened to the atmosphere. our boiler is just not big enough to handle the load of 15 railcars thats why i was thinking of reducing the pressure but i think thats a lost cause.
RE: steam pressure reducing from 180psi to 80psi
This minimises the energy that you have to put into the steam which would otherwise be lost once the steam condenses and is blown off through the steam trap (I'm not familiar with a "thermal dynamic steam trap"- so I'm just assuming that once the steam has condensed- the condy will be blown down through the trap).
Now obviously because you ARE going to lose heat through the boiler and the rail cars- your going to want to run a higher temperature to heat the rail cars up faster. The actual temp you want to run at will be a trade off between faster heating (and higher energy losses due to condy blow down) vs faster heat up time and reduced thermal losses.
Looks like you're already part way to that optimisation process because you've noticed a decrease in gas consumption when you first dropped your boiler operating pressure.
RE: steam pressure reducing from 180psi to 80psi
running at 85 psig will always be less expensive from a utility viewpoint.
your boiler should have lower temperatures in the exhaust and all your steam leaks and bad traps will not dump as much steam as well.
either accept the lower heating rates or pay the higher prices.
and for the railcars, are you using wild, live steam for internal coils or are the internal coils trapped? the rail car coils should be equipped with traps.