Ammonia compressor systems

Figure 26 shows a packaged ammonia compressor system designed for servicing an SSHE in margarine production. The system is skid-mounted from the factory for easy installation. Only the condenser of the system is supplied loose. 

Ammonia compressor systems used in margarine plants are usually equipped with highly efficient superseparators for removal of lubrication oil from the... 

Figure 26. Packaged ammonia compressor system. Courtesy of Cremeria Americana SA, Mexico.

There has been some innovative technology applied by some wineries to maintain the wines in a warm condition. Several wineries have been visited where small tanks, puncheons, or barrels were covered with electric blankets to maintain an adequate temperature for the malo-lactic fermentation. Larger wineries utilize an external heat source to warm the storage tanks in which the red wine is held. Where wineries are using ammonia refrigeration systems directly in the jacketed portion of the fermentors, these systems can be used as a heat pump. The hot ammonia gas from the compressors is desuperheated and the tank jacket used as a condenser to condense this gaseous ammonia. This has proven to be a very effective means of warming a tank. 

The loop pressure has an important influence on the performance of the ammonia synthesis loop because of its influence on the reaction equilibrium, reaction kinetics, and gas/liquid equilibrium in the product separation. Actual selection of loop pressure is in many cases a compromise between selecting a high pressure to favour the ammonia synthesis reaction, and on the other hand selecting a reasonable pressure to minimise the compression power of the synthesis gas compressor, which compresses the synthesis gas to the desired loop pressure. The loop pressure also has a significant impact on the ammonia refrigeration system, since a high loop pressure favours condensation of the ammonia product in the loop water cooler and saves compression power on the refrigeration compressor. On the other hand, a low loop pressure saves compression power on the synthesis gas compressor, but increases the... 

A typical conventional ammonia plant (1500 t/d) has steam turbines with a power output of 35 MW. The syngas compressor and the ammonia compressor in the chiller system are the largest eonsumers. There is a flat minimum of compressor power at a synthesis pressure of approximately 150 bar [169]. 

Optimize ammonia refrigeration systems with thermosyphon compressor coohng, liquid overfeed evaporators, pumped refrigerant circulation, and automatic air purgers. 

In the early days of ammonia manufacture, the average lifetime of the ammonia synthesis catalyst was limited to a few years, while today, lifetimes in excess of 10 years are common. This dramatic increase arises from a number of improvements. Most noteworthy are the introduction of centrifugal compressors and the application of lubrication oils with low sulfur content as outlined by Nielsen. Another significant improvement is the incorporation of a secondary ammonia condensation system, in which the make-up gas together with the recirculating gas is washed in liquid ammonia before entering the ammonia synthesis converter (see Fig. 8.1). 

Ammonia has low miscibility in mineral oils, alkylbenzenes, and polyol ester lubricants, particularly at low temperatures. A typical ammonia system uses a coalescing separator that removes all oil in droplet or aerosol form and drains it back to the compressor. Sometimes separators are equipped with some means of cooling the discharge gas to condense any oil that is discharged as a vapor. 

This ammonia is recycled to the reactor via a compressor and a heater. Liquid ammonia is used as reflux on the top of the absorber. The net amount of carbon dioxide formed in the reactor is removed as bottom product from the absorber in the form of a weak ammonium carbamate solution, which is concentrated in a desorber-washing column system. The bottom product of this washing column is a concentrated ammonium carbamate solution which is reprocessed in a urea plant. The top product, pure ammonia, is Hquefted and used as reflux together with Hquid makeup ammonia. The desorber bottom product, practically pure water, is used in the quench system in addition to the recycled mother Hquor. 

During each of the three phases a refrigeration system, consisting of three (3) compressors, two (2) condensers and one (1) separation drum, ensures that the ammonia is at its storage temperature. 

Cold suction gas provides cooling for the compressor and is sufficient to keep small machines at an acceptable working temperature. Refrigerantshaving high discharge temperatures (mainly ammonia) require the use of water-cooled cylinder heads. Oil coolers are needed under some working conditions which will be specified by the manufacturer. These maybe water cooled or take refrigerant from the system. 

When produced from natural gas the synthesis gas will be impure, containing up to 5 per cent inerts, mainly methane and argon. The reaction equilibrium and rate are favoured by high pressure. The conversion is low, about 15 per cent and so, after removal of the ammonia produced, the gas is recycled to the converter inlet. A typical process would consist of a converter (reactor) operating at 350 bar a refrigerated system to condense out the ammonia product from the recycle loop and compressors to compress the feed and recycle gas. A purge is taken from the recycle loop to keep the inert concentration in the recycle gas at an acceptable level. 

For the three-compressor refrigeration system using ammonia ... 

In a vapor-absorption refrigeration system, there are no moving parts. The added energy comes from a gas or liquid fuel burner or from an electrical heater, as heat. rather than from a compressor, as work. See Fig. 2. The refrigerant used in this example is ammonia gas. which is liberated from a water solution and transported from one region to another by the aid of hydrogen, The total pressure throughout the system is constant and therefore no valves axe needed. 

Accidental connection of an oxygen cylinder to top-up an ammonia-containing refrigeration system led to explosive destruction of the compressor. 

The chilled water (7°C) for the absorber is supplied by an absorption refrigeration unit, using heat recovered from the compressor intercooler as the energy source. Heat for ammonia vaporization, as previously noted, is available at 35°C and is recovered from the secondary gas cooler. The system uses circulating condensate as the energy transfer medium. 

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