Atmospheric Storage of Ammonia

[asif]

I need design and selection related literature on ammonia refrigeration package that will liquefy the vapor generated from ammonia storage tank. How we can calculate the refrigeration duty of the whole package. Please help

Please start a new thread in the industrial forums please.

[GrantD]

Hi Asif,

Your request is very vague. Can you give more specs. on what you have and what you want to do?

Grant

[US Iceman]

Can you give more specs. on what you have and what you want to do?

I think he wants to know how to condense ammonia vapor in an atmospheric ammonia storage sphere.

An atmospheric ammonia storage tank is not related to a NH3 recirculation system. These are two different types of systems.

[TXiceman]

Asif, as soon as you post in the correct forum with a new thread, I'll give you some insight into calculating the load on a amoonia storage tank.

USiceman, can you move the post to the correct forum?

Ken

[US Iceman]

OK guys, all set. Have at it!

[smpsmp45]

It must be Horton Sphere. We used to do such jobs for fertilizer companies & ammunition factories.

[TXiceman]

I have worked on several atmospheric ammonia storage systems over the years. You need to first determine all of the loads and streams coming to the tank.

Your tank can be used for a rail tank car, barge, pipe line unloading/loading or direct from a process plant.

Your tank loads are broken down into the following major categories:
-heat gain.
-vapor displacement (from an unloading pump)
-flash load from condensed refrigerant.
-flash load and vapor displacement from any plant loads
-flash load from loading of a barge or rail car.

The easiest way to keep track of the loads is to draw a Control Volume around the tank and then do a:
-Mass balance on the flows
-Energy balance on the tank.

Start solving for flows and work you way through the set of equations and know valves to calculate the unknown flows. If you are not familiar with the basics of thermodynamics, you will need some help here. I am afraid that there are no short cut methods or computer programs available for free. It is back to basic thermodynamics and heat transfer.

The heat gain on the tank should be available from the tank manufacturer, so ask him for this data.

The next critical issue is you add up all of the flow streams from the tank to the compressor(s).

The smaller flows are the ones from the heat gain and the flash from condensing. The larger flows will be from the vapor displacement during pumped unloading to the tank.

A critical issue is the actual temperature to the compressor(s) from the tank. If will seldom be at saturation conditions. When the tank is full and during cooler weather the tank vapors will be much cooler and may only have 10 dF of superheat. In the hot months and the tank level is low, the vapor in the tank will be much warmer. I have seen vapor coming off of a low level tank in the summer in Texas as hot as 75 dF (this amounts to about 100 dF of superheat. The compressors are not designed to handle this hot of a suction, so you need to make arrangements in the design and load to handle the excessive suction line heat.

An easy way to do this is provide a suction trap with small boil out coil in the bottom (yes, you need a suction trap/accumulator) and a spray nozzle in the suction just ahead of the trap to keep the suction heat to a range that can be tolerated by the compressor(s). The high suction superheat can cause the compressor to shut down on high oil temperature or high discharge temperature. It also lowers the mas pumping rate of the compressor since the specific volume of the suction gas is much higher and results in higher volume flow for the compressor and thus reduced capacity.

You will not be able to design and rate the system based on tons, BTUH, kiloWatts, or kilocalories, but will have to design and rate the compressor based on mass and volume flow rates.

You also need to review the design cases to see how many hours you will be spending in each case to determine if you need a single or multiple compressors to have an efficient design. I have put in systems with as many as 3 compressors that were staged on according to how the tank was being loaded or off loaded. One compressor carried it through a lot of days where there was only a heat gain and no loading. Two compressors were used if there was a rail car unloaded and if they unloaded from a barge, it took three compressors.

Hope this sheds some light on the issues involved in the load calculation for an ammonia storage system.

Ken

[US Iceman]

It is back to basic thermodynamics and heat transfer.

Yeah, this is one of those applications where you need to do real engineering with a calculator (or slide rule, depending on age), pencil, and paper. They can be involved with all the different calculations, not to mention the control system trying to maintain the sphere pressure within a small margin of error against atmospheric pressure.

I've worked on one or two of these also. It's a very interesting process. The only thing that is measured in Tons is the amount of ammonia in the tank(s).

[TXiceman]

I forgot to add the purger. Some smaller plants can get by with a small standard purger, but in a larger off loading facility, you will get a fair amount of inerts in the condenser and have to use a large custom built purge system that will probably be an additional 10 or 15 ton load on the compressor.

It is basically a pretty specialized type of engineering. You need to contract with a consulting engineer that has handled a storage facility before.

Ken

[asif]

Dear All, this is a great effort from your end i would like to simplify the issue
1. Double wall storage tank of 500 Met capacity, design temperature -33C and pressure 0.153Kg/cm2g and operating pressure 0.051Kg/cm2g, design boil off 0.05% of capacity
2.I want to know how to calculate the heat ingress into piping and heat ingress from transfer pumps to the liquid ammonia.
3.Liquid withdrawal from tank 139m3/hr, vapor withdrawal approx. 226m3/hr
4.Liquid innage 49m3/hr, vapor innage 50m3/hr
3.What will be impact of vapor temperature on compressor performance and refrigeration duty if it increased from -33C to -27C at the suction of refrigeration compressor (screw)

Please share standards or design practices for this industrial refrigeration system

[asif]

1.Further this is a static storage tank 2.Length of line transferring ammonia from ammonia plant to tank is 500m & 4 inch dia
3.Length of suction line to transfer pumps is 50m & dia 8 inch (supply liquid ammonia during plant shut down,
4.Ammonia Transfer pump minimum flow line 50m, 3 inch dia open in tank

Hoping after sharing all these info you people definitely help out me

[asif]

Let me guide in selection of refrigeration system for ammonia we should give the minimum design temperature (-33C) or maximum actual temperature (-27C) to the vendors of refrigeration unit for selection of compressors, condenser and evaporator. Which temperature will be more advantageous and why.

[US Iceman]

Let me guide in selection of refrigeration system for ammonia we should give the minimum design temperature (-33C) or maximum actual temperature (-27C) to the vendors of refrigeration unit for selection of compressors, condenser and evaporator. Which temperature will be more advantageous and why.

You have to maintain the suction pressure of the compressor to control the pressure within the storage sphere. Even though the compressor controls the pressure the vapor can still be superheated (either at the dome of the storage sphere or through the piping from the sphere to the compressor).

What you will find is the vapor is superheated at whatever pressure you need to maintain when the vapor arrives at the compressor.

You need to do the heat transfer calculations for the suction line from the storage sphere to the compressor. This line can pick up a lot of heat. Sometimes this superheat is minimized by de-superheating it before it flows into the compressor. This helps to prevent high oil cooling loads and discharge temperatures for the compressors.

[TXiceman]

Asif, this is a lot deeper problem that it appears you are ready to handle. I certainly would not want to tackle such a project without having worked with an engineer that has done this type design before. There is too much risk of safety to go blindly into this type project. I know of several consultants in the US that can do the design, however you will need to pay for the knowledge.

US Iceman or I can do the design, but it is a lot of manual calculations and back to the very basics of heat transfer and thermodynamics. I currently do not perform consulting work but can provide the names of others.

This is a highly specialized field that requires knowledge of the design to provide a safe design. I do not know of any one that will carte-blanch provide you with the design. We have provide you the basis for a design to start.

Sorry to be so harsh, but I have been working with ammonia and ammonia plants for almost 40 years now.

Ken

[US Iceman]

This is a highly specialized field that requires knowledge of the design to provide a safe design.

Isn't that the truth? This is not one of the jobs you start on as a beginner.

Even though I've worked on a few, I would not now in today's lawyer environment. The risk exposure is too high...

[asif]

if you have previous working please share with me