HOT! Free Download The Steam And Condensate Loop Book
Kenneth Calimlim
This Module of The Steam and Condensate Loop is intended to give a brief, non-technical overview of the steam plant. It offers an overall explanation of how the different parts of the steam plant relate to each other - and represents useful reading for anyone who is unfamiliar with the topic, prior to progressing to the next Block, or, indeed, before undertaking any form of detailed study of steam theory or steam plant equipment.
The hot gases from the burner pass backwards and forwards up to 3 times through a series of tubes to gain the maximum transfer of heat through the tube surfaces to the surrounding boiler water. Once the water reaches saturation temperature (the temperature at which it will boil at that pressure) bubbles of steam are produced, which rise to the water surface and burst. The steam is released into the space above, ready to enter the steam system. The stop or crown valve isolates the boiler and its steam pressure from the process or plant.
If steam is pressurised, it will occupy less space. Steam boilers are usually operated under pressure, so that more steam can be produced by a smaller boiler and transferred to the point of use using small bore pipework. When required, the steam pressure is reduced at the point of use.
As long as the amount of steam being produced in the boiler is as great as that leaving the boiler, the boiler will remain pressurised. The burner will operate to maintain the correct pressure. This also maintains the correct steam temperature, because the pressure and temperature of saturated steam are directly related.
Ordinary untreated potable water is not entirely suitable for boilers and can quickly cause them to foam and scale up. The boiler would become less efficient and the steam would become dirty and wet. The life of the boiler would also be reduced.
Other impurities remain in the boiler water after treatment in the form of dissolved solids. Their concentration will increase as the boiler produces steam and consequently the boiler needs to be regularly purged of some of its contents to reduce the concentration. This is called control of total dissolved solids (TDS control). This process can be carried out by an automatic system which uses either a probe inside the boiler, or a small sensor chamber containing a sample of boiler water, to measure the TDS level in the boiler. Once the TDS level reaches a set point, a controller signals the blowdown valve to open for a set period of time. The lost water is replaced by feedwater with a lower TDS concentration, consequently the overall boiler TDS is reduced.
If the water level inside the boiler were not carefully controlled, the consequences could be catastrophic. If the water level drops too low and the boiler tubes are exposed, the boiler tubes could overheat and fail, causing an explosion. If the water level becomes too high, water could enter the steam system and upset the process.
The steam generated in the boiler must be conveyed through the pipework to the point where its heat energy is required. Initially there will be one or more main pipes or steam mains which carry steam from the boiler in the general direction of the steam using plant. Smaller branch pipes can then distribute the steam to the individual pieces of equipment.
It is important to ensure that the steam leaving the boiler is delivered to the process in the right condition. To achieve this the pipework which carries the steam around the plant normally incorporates strainers, separators and steam traps.
A strainer is a form of sieve in the pipeline. It contains a mesh through which the steam must pass. Any passing debris will be retained by the mesh. A strainer should regularly be cleaned to avoid blockage.
The steam should be as dry as possible to ensure it is carrying heat effectively. A separator is a body in the pipeline which contains a series of plates or baffles which interrupt the path of the steam. The steam hits the plates, and any drops of moisture in the steam collect on them, before draining from the bottom of the separator.
Steam passes from the boiler into the steam mains. Initially the pipework is cold and heat is transferred to it from the steam. The air surrounding the pipes is also cooler than the steam, so the pipework will begin to lose heat to the air. Insulation fitted around the pipe will reduce this heat loss considerably.
When steam from the distribution system enters the steam using equipment the steam will again give up energy by: a) warming up the equipment and b) continuing to transfer heat to the process. As steam loses heat, it turns back into water. Inevitably the steam begins to do this as soon as it leaves the
boiler. The water which forms is known as condensate, which tends to run to the bottom of the pipe and is carried along with the steam flow. This must be removed from the lowest points in the distribution pipework for several reasons:
As mentioned before, steam is usually generated at high pressure, and the pressure may have to be reduced at the point of use, either because of the pressure limitations of the plant, or the temperature limitations of the process.
Control valves are used to control the flow of steam. The actuator, see Figure 1.3.6, is the device that applies the force to open or close the valve. A sensor monitors conditions in the process, and transmits information to the controller. The controller compares the process condition with the set value and sends a corrective signal to the actuator, which adjusts the valve setting.
Often, the condensate which forms will drain easily out of the plant through a steam trap. The condensate enters the condensate drainage system. If it is contaminated, it will probably be sent to drain. If not, the valuable heat energy it contains can be retained by returning it to the boiler feedtank. This also saves on water and water treatment costs.
Sometimes a vacuum may form inside the steam using plant. This hinders condensate drainage, but proper drainage from the steam space maintains the effectiveness of the plant. The condensate may then have to be pumped out.
Mechanical (steam powered) pumps are used for this purpose. These, or electric powered pumps, are used to lift the condensate back to the boiler feedtank.
A mechanical pump, see Figure 1.3.7, is shown draining an item of plant. As can be seen, the steam and condensate system represents a continuous loop.
Once the condensate reaches the feedtank, it becomes available to the boiler for recycling.
This essential book explains the principles of steam engineering and heat transfer, covering all aspects of steam and condensate systems from the boiler house, through the steam distribution system to the point of use, and recovering, and returning condensate back to the boiler.
Optimizing your plant through best practice energy saving principles can greatly reduce your carbon emissions.
With practical application knowledge to deliver energy saving solutions, this indispensable reference guide is a must for all experienced engineers and an invaluable training tool to all those new to steam engineering.
Thanks for the reply.
The condensate loop ran the full length of the basement and feed a few radiators and was hooked up to an electric pump. It looked like it was done after the steam part of the system was installed. I just cut it off where they had attached it to the original piping.
Yes, if I don't have an auto feeder the tenant will have to fill boiler.
Just remember......Any tenant will now have that job. You have to teach them how, and instruct them to contact you if they are having to add water often. They have to know, to not add water to an empty sight-glass, or they can get killed. Does the boiler have a probe-type, or float LWCO?
Did you remove the aquastat from the boiler for the hot water loop?
I'd put a probe-type on it. The float type have to be maintained. They get gummed up. Look at Hydrolevels products for water feeders. They have a counter, so you know how much water has been added. Stay away from the ones with Cycleguard feature. It's a stupid feature that shuts the boiler off to let condensate return. The steam pros at Heatinghelp.com can tell you exactly what to use. You'll get different opinions about whether or not to use an auto-feeder. Because it's a rental I'd use it. I'd also keep tabs on the water used.
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See if there is any(enough) main vents. If you have any buried wet returns, you might want to pressure test them. At the very least flush the wet returns. You really should get a steam man in there. Not all plumbers know what they are doing when it comes to steam. You want everything squared away, now, so you don't get the phone calls.
I am modeling a lab building with a lot of equipment like steam sterilizers with direct steam consumption. I added steam equipment loads in the spaces and I am getting the MBtu's of steam consumed by the building in the OpenStudio output. However, I want the output in terms of natural gas used to produce that steam. Is there a way I can model a plant loop, add these steam equipment loads on the supply side and have a natural gas fired boiler producing steam on the demand side ? How can this be done in OpenStudio? Or is there any other way I can model steam consumption in spaces and natural gas consumption as the output?
If you are using the DistrictHeating fuel for something else than your steam equipment, make sure you fill in the SteamEquipments' End-use subcategory, so you can easily only get the consumption for these steam equipment.
Steam systems are not supported in OpenStudio. There is only one component you'd need that is implemented (Boiler:Steam), but others are not (PumpVariable:Speed:Condensate, Pipe:Adiabatic:Steam, all the steam components such as Coil:Heating:Steam etc). This is why the steam boiler is not yet included in the HVAC library.
Thanks for the answer @Julien. 19k karma points is amazing! After you short derivation, I read about the fraction lost/radiant/latent terms and I understand those better now. As for the the steam equipment, there is an option to change the fluid type to steam in the plant loop, but I assume that wouldn't be very useful as of now?
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