New Process Steam Application

L'town Radiant_2

Hey folks... I do a lot how water system design, and consider myself dangerously knowledgeable about low pressure steam systems. I have been asked to put together steam system for a local business that cleans and drys animal wool. They have large conveyor dryer machine that pulls air over a bank of steam coils. This is the only use for the steam, there is just one inlet and outlet connection. We expect to operate at about 2psi. The equipment is only about 15ft from the boiler and they are on the same grade. The drawing I have attached seems too simple to me, I feel like I am missing something. Would you wise steam heads out there take a look at this and offer your constructive criticism?

Abracadabra

1 - use a drop header
2 - use 3" risers
3 - place main vent after coil

Why are you adding in a boiler feed pump? I prefer to avoid pumps on steam systems if possible. If you are worried about water capacity, you might be able to get away with a condensate reservoir. What's the EDR of the dryer coil? How did you size the boiler?

Steamhead

What is your "B" dimension (height between the boiler's waterline and the trap on the coil outlet?

nicholas bonham-carter

If the steam coils are within the "A" dimension, you will need very low pressure (2 ounces)-regulated by a vaporstat, and verified with a 15 ounce gauge. No condensate tank should be needed. Pay attention to the EDR of the coil for sizing purposes of the boiler.--NBC

GW

Why is an F and T needed, there are no other returns to mess with it.

EBEBRATT-Ed

As Steamhead said you need to check the "B" dimension and if you have it you can do away with the steam trap and feed tank. You probably don't have it so you will need the trap and feed tank.

When you come out of the steam coil you need to drop down with a 90 full size of the coil at least 1 foot then put a tee coming out the side the size of your trap. Put a cap and a nipple in the tee for a dirt leg. If you don't drop down and instead go straight into the trap the bottom of the coil will remain waterlogged and not heat well while the trap "decides" weather it has water or steam. Traps cycle

Also pipe a vacuum breaker on a tee on the coil inlet (or use a check valve) to let air in the coil when the steam collapses. Especially if the coil has a control valve

A vent and an overflow on the boiler feed tank will be needed

nicholas bonham-carter

The vent (Gorton 2) will take care of letting the air out, and in.
There is really no need for a condensate tank, or a trap, as there will be no lag in the condensate coming back, if properly piped.--NBC

Larry_52

Not a fan of vacuum breakers for protecting coils from stall. Can cause pitting the condensate system long term. Although I don't see the TCV on the inlet coil in the drawing. There is the spirax APT trap that Can be used for treating stall conditions. Psi would need to be higher than 2 psi for this type of TCV process control.

Which brings me to the next question what will be the process control, set point and how much deviation from process can there be? What kind of approach air temp is the exchanger going to be dealing with and how much does it vary?

why the change from hot air exchange, seems more practical in this case. (Assumed from the X'd out furnace)

nicholas bonham-carter

I'm not sure what you mean by stall, but a good main vent will take care of any vacuum conditions, and in this case the boiler will be sized to run constantly at low pressure, to keep the wet return from filling up with water from over pressure.--NBC

Larry_52

Stall is the term used for negative trap differential on steam heat exchangers. I was using it in reference to Ed's description of an inlet TCV, which would require the pump and IMO a pump trap.

My concern as per the drawing is cycling on boiler psi diff. You could end up with a real "bungee cord" air temp process control, if the load sizing is off or load rate changes are quick...

Henry

Here is the supply piping for a small distillery. Notice the drop headder and the future connections! Unfortunatly, the customer prebought the boiler and it does not have any pickup. Therefore he will have to use one piece of equipment at a time untill the steam pressure stays constant, then the next but not everything at the same time.

Henry

Steam coils in industry vary in pressure from 12 to 30 PSI depending on the aplication, sometime higher. We put the air vent (thermostatic trap) on the return as shown by the dotted piping. IMO, 2 psi for process will not cut it. The heat exchange surface will excessively large.

nicholas bonham-carter

Unlike a steam kettle, where large amounts of liquid are suddenly required to be heated, I can't see much variation in load with a blower, and steam coil.
What is the desired exit air temperature? Probably not too hot for drying wool.
How about running this system sub-atmospherically?--NBC

Henry

It will not work in industrial apllications

Henry

Here is something that I have seen a number of times. The boiler is sized without the pickup factor in an industrial application. They raise the pressure from 30 or 75 PSI to 125 PSI expecting to get more steam. NO! You get less pounds of steam. Boiler steam output of pounds of steam is at 0 PSI!

Larry_52

Henry said:

It will not work in industrial apllications

x2 was trying to lead gently into that.

L'town Radiant_2

Wow! Lot's of good feedback here. Thanks for the help to all of you. Let me take your comments one at a time:

Abracadabra: I will definitely recommend a drop header, it's just hard to draw it with my simple drawing program. The 2-1/2in risers were sized based on what Weil Mclain suggested, but I have no issue with 3in either. Main vent after coil...ok. I would prefer to get rid of the pump too, but didn't know if I should. The EDR of the coils is 1,448 and was provided by the equipment manufacturer.

Steamhead: That's a great point. The condensate outlet of the equipment is at about 5ft, the water line of the boiler is 2ft.

nicholas bonham-carter: Looks like the heating coils will definitely be within the A dimension...

GW: So you think no trap at all, or just a bucket trap. I thought F&T would be better at getting rid of air..

EBEBRATT-Ed: You're right I don't clear demension B, guess I'll keep the trap and feed tank with the piping that you suggest...?

nicholas bonham-carter: Guess we need to clarify if this trap and tank are really necessary or not!

Larry: I am uncertain on the controls just yet, I assume just a two way control valve infront of the coils. A set of contacts could be made to open the valve and bring in the boiler gas valve. once the equipment is on it runs most all day and they'll take all the heat they can get, so it's really a matter of on/off and not set point. the inlet air temps can range anywhere between 50 and 80 degrees.... ignore that xed out furnace, just bad drawing template..

L'town Radiant_2

Henry, Thanks for the drawings. So I am confused, do you think I'm better off at the low pressure operation or something close to 15psi? I don't think they would want see anything more than 200deg air...

EBEBRATT-Ed

If you have a control valve you will need the vacuum breaker or the induced vacuum in the coil when the control valve shuts will cause the condensate to hang up in the coil. I would recommend the boiler feed tank as I think a pumping trap would not have enough storage. Even though the system is close coupled your going to get some lag time between steaming time and condensate return.

Low pressure steam has more latent heat/lb so the lower you run the steam pressure the better, however this may depend on how the coil was selected. If you need an air temp higher than 212 you will have to raise the steam pressure until you get their.

I would check with the equipment mfg. for steam pressure/temperature and lb of steam required befor going further jmho

Larry_52

It is basically impossible to achieve 212 degree air from 1psi steam on a coil