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Large Propane Consuming Systems

This Chapter contains information on:

• Grain Dryer with Built-In Vaporizer
• Grain Dryers
• Vaporizers
• Propane Vapor Grain Dryers
• Testing Procedure- Mitchell Vaporizers
• Repair Procedures- Mitchell Vaporizers
• Algas 40/40 and 80/40 Vaporizers
• Should a Regulator Be Installed at the Tank on Grain Dryers?
• Freeze-Ups
• Vapor Dropping Back to Liquid and be Controlled

Grain Dryer with Built-In Vaporizer

When changing liquid propane to vapor propane in high capacity grain dryer with built-in vaporizer, a residue may form due to heat being applied to the liquid propane to change it from liquid to a vapor, in order to satisfy the high volume of BTU needed by the burner. The residue is a dark brown material that may settle on regulator or temperature sensing control and cause them to have a intermittent operation. Research has found that the residue comes from the inside lining of hose used to transfer liquid propane. Where this condition exists, it is suggested a drip be installed between central and where the vapor leaves the vaporizer section of the dryer. The operator should periodically open the valve at bottom of the drip to drain off residue.

Grain Dryers

Grain dryers are classified by two types--liquid and vapor, which tells us what type of supply is needed from the propane supply tank.

A liquid dryer will have a built-in vaporizer with the supply from the tank being liquid and converted to vapor in the dryer burner chamber before it enters the regulator and dryer controls going to the main burner as a vapor.

A vapor dryer takes the vapor from the top of the supply tank and passes it through a regulator and controls to the main burner. This dryer depends upon the tank for natural vaporization. Refer to Chapter 4 for size of tank required to meet vapor pressure demand.

We recommend regulators at the tank and at the dryer in both types of propane supply. A regulator at the tank will reduce the possibility of freeze-up, surging, and vapor returning to liquid under certain conditions.

1. Liquid regulators are recommended to control tank pressure for tank pressure to a 5 to 35 psi or 30 to 60 psi. They will be limited to 130 to 450 gallon propane flow per hour.
2. Vapor regulators are recommended for 5 to 35 psi or 30 to 60 psi. They will be limited to 2,500,000 BTU to 12,000,000 BTU per hour.

For higher BTU gallon or vapor applications, call the GROWMARK, Engineering Department of E.A.R.S.

It is recommended that all high pressure regulators be set at about 10 lbs. Higher than the dryer pressure demand.

Vaporizers

Where the tank cannot supply enough vapor to supply the burner demand, a vaporizer can be used. Call GROWMARK, Engineering Department of E.A.R.S. for recommendations on the Algas, Mitchell or Ely (Water Bath Vaporizers). Several models are available meeting needs of various vapor demands.

Propane Vapor Grain Dryers

Some grain dryer manufactures are requiring that their dryers be hooked up at tank pressure. They do not want a regulator installed at the tank. When this is done at the vapor service valve, the system will not be protected by an excess flow valve.

It is recommended that an in-line excess flow valve , Rego 2115B, ¾" female by ¾" female N.P.T. be installed. This will protect the system in the event of line failure down stream from the service vapor valve.

Special Safety Recommendations for Liquid Grain Dryer Hook-Ups When Using Fisher Saf-E-Vac or Rego Check-Loc Valves

In the event of hose or copper tubing failures, the excess flow valves in the Saf-E-Vac or Check-Loc may not close due to small size hose or tubing used to supply a grain dryer. We recommend following NFPA Pamphlet 58 and not use the above valves, but use the Liquid Withdrawal Valve from the storage tank top.

When connecting liquid withdrawal piping at the tank, to supply the any Liquid Withdrawal Burner, it may be impossible to secure an excess flow valve with a low enough closing rate to protect the system. Therefore, we suggest compliance with NFPA Pamphlet 58, 3-3.1

Testing Procedure—Mitchell Vaporizer

When liquid propane is suspected of passing through the vaporizer into the appliance burner, liquid in supply pipe would cause the pressure gauge located down stream from the second stage regulator to increase pressure rapidly when burners shut off by automatic controls.

The following procedure is recommended to determine if the condition is caused by the vaporizer or the supply tank, and which vaporizer is at fault….

1. Close vapor valve at supply tank or tanks.
2. Shut off vaporizer burner by closing vaporizer burner supply valve.
3. With appliance burner operating, frost will appear on the left hand tubing and vaporizer chamber surplus flow valve at once when liquid is passing through the vaporizer. If frost appears, close appliance supply valve at once as liquid is coming through the surplus flow valve going to the burner. This means the vaporizer is in need of repair. Refer to below, Repair Procedure-Mitchell Vaporizers. If no frost appears, vaporizer is okay and appliance burner will go out, as supply has been closed off.
4. When indication of liquid in supply line is still present and no frost appears at vaporizer connection….

1. The supply tanks could have been overfilled, filled vapor lines with liquid
2. The internal vapor pipe, or connections in tank, when internal vapor is used, have a leak which would cause vapor lines to be filled with liquid and would pass into supply lines along with vapor from vaporizers that were operating in a normal manner.

Repair Procedure—Mitchell Vaporizers—30 & 70 Surplus Flow Valve Liquid Leak

1. Close appliance burner supply valve.
2. Close vapor valve at supply tank.
3. As soon as vaporizer burner shuts off by the control, close liquid supply valves at supply tank. All liquid should be pushed back into the supply tank at this time. You should find very little product when pipe connections are broken t vaporizers.
4. Remove vaporizer cabinet top by removing two large nuts at relief valves.
5. Remove two flare nuts on pipes from left surplus flow valve assembly.
6. Remove four nuts holding surplus flow valve assembly and remove top section of surplus flow valve assembly.
7. Remove double nuts on float shaft.
8. Remove lower section of surplus flow valve assembly.
9. Replace "O" Ring in bottom of lower section of surplus flow valve assembly.
10. Replace lead gaskets when needed.
11. Repeat procedure on Model 70 right-hand surplus flow valve.
12. In 99% of the cases, this will correct the condition. If not, the floats have developed a leak or have collapsed. In either case, contact GROWMARK, Engineering Department of E.A.R.S.

Mitchell Part Numbers:  Mitchell V244 - "O" Ring Seal,   Mitchell V-201- 2 Aluminum Gaskets

See illustration of the Mitchell Vaporizer system and its parts.

Algas 40/40 and 80/40 Vaporizers

The Algas Propane Vaporizer is another product used to produce propane vapor required above is required from the propane storage container. The Algas requires little maintenance and have few working parts. Many are in the system and have been operating for years with only a yearly cleaning and replacements of valve kits for maximum efficiency.

Should A Regulator Be Installed At the Tank On Grain Dryers?

The answer is YES for the following reasons:

1. Less freeze-ups.
2. Vapor dropping back to liquid can be controlled.

A. FREEZE-UPS- can happen at temperatures above 32° F, as Propane has the same refrigeration characteristics as Freon 12 or 22 in that when these products have a pressure drop across an orifice, such as we do in a regulator at the grain dryer burner, a refrigeration process takes place. If moisture droplets are present, it could freeze, blocking or restricting the orifice. A regulator at the tank will lessen the possibility, as we have a colder condition with a high drop in pressure than we do with a low drop in pressure. Example…..

1. Outside temperature of 40° F…tank pressure is 72 lbs. Grain dryer operating at 3 lbs. Drop across the regulator orifice is 69 lbs.
2. Regulator at tank reducing pressure to 15 lbs. Grain dryer operating at 3 lbs. Drop across regulator orifice is 12 lbs.

There is a greater chance of freezing in example #1, as the drop across the regulator orifice is greater, causing the orifice area to be colder.

B. VAPOR DROPPING BACK TO LIQUID CAN BE CONTROLLED

The above can happen any time you have the right condition present, such as tank pressure at outside temperature. On the chart below, find that at 10 lbs. tank regulator pressure and a -10° F temperature, with piping exposed to outside temperature, you could have vapor returning to liquid in the piping. Lowering the tank regulator pressure to 8 lbs. would change the Dew-Point or vapor returning to liquid to a -25° F temperature equivalent. Therefore, by changing one factor—pressure—(you have no control over the temperature), you can change the Dew-Point of conditions for vapor returning to liquid to a lower temperature.

Some grain dryer manufacturers do not want a regulator installed at the tank. What happens at higher outside temperatures when a tank without a regulator is used and the patron is drying corn on a 55° F day? The Dew-Point would be at 85 lbs. Pressure. With product temperature at 50° F, the vapor pressure on the tank will be 86 lbs.; with this condition, vapor would drop back to liquid.

In all Propane storage tanks, the product temperature will be 5° F to 10° F lower than the outside temperature, due to cool nights. Therefore, on a 55° F day, we have the ideal conditions for Dew-Point of vapor return to liquid. This condition can exist any time the pressure and temperature meet on the Dew-Point curve on the chart. With a regulator on the tank, you can reduce the pressure and remove the possibility of vapor dropping back to liquid.

Refer to the attached chart to avoid Dew-Point situations when you will experience large demands when the temperature will equal tank pressures.

REMEMBER….Change the pressure to a lower pressure and you can reduce the temperature at which vapor will return to liquid in the pipe system. This can cause a surging in many systems.

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