Integrated Ammonia Synthesis Plants

Single train plants are economic to operate, since the waste heat can be optimally utilized and the personnel requirements are 

The economics of NHi-plants is very dependent upon the plant size 

Storage and transport of NH3 occurs at various pressures and temperatures 

In single-train plants it is necessary to store a certain amount of ammonia to cover production breakdowns. The ammonia is either stored at atmospheric pressure and low temperatures (-33°C), or under moderate pressures at -f5 to -5°C. Ammonia is also transported under these different conditions. 

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Integration of HWP with the ammonia synthesis plant Purified synthesis gas after the pressure adjustment is sent to HWP, which acts as a by-pass to the ammonia synthesis unit. ... 

Urea s expanding production has thus been closely tied with increasing synthesis and application of nitrogen fertilizers in the rice-growing countries of Asia. In 1960 less than 10% of the world s nitrogen fixed by the Haber-Bosch process was converted to urea the share reached 15% in 1968, doubled to 30% by 1973, and in 1997 stood above 46%. China, India, Indonesia, and Pakistan are the world s largest urea producers, and most of the new ammonia capacity is directly tied to urea synthesis in integrated ammonia-urea plants. ... 

Integrated ammonia-urea plants use the recovered CO2 in the subsequent synthesis of urea other CO2 uses include carbonating soft beverages and pumping the gas into oil wells to enhance crude oil recovery. 

Further treatments of the gases mainly involve cooling, conversion of CO into C02 and H2, absorption of C02, etc. Generally such processes are carried out in integrated plants where hydrogen is used for instance for ammonia synthesis, petrochemical work, etc. 

An operating ammonia plant using the aforementioned improvements is shown schematically in Fig. 1. This plant8 has a capacity of 1000 short tons/day (900 metric tons/day) and uses natural gas as feedstock. The plant can be divided into the following integrated-process sections (a) synthesis-gas preparation (b) synthesis-gas purification and (c> compression and ammonia synthesis. A typical (Kellogg designed) ammonia plant is shown in Fig. 2. 

Knowledge of the reaction kinetics is important for designing industrial ammonia synthesis reactors, for determining the optimal operating conditions, and for computer control of ammonia plants. This means predicting the technical dependence on operating variables of the rate of formation of ammonia in an integral catalyst volume element of a converter. 

The choice of a specific CO2 removal system depends on the overall ammonia plant design and process integration. Important considerations include CO2 sHp required, CO2 partial pressure in the synthesis gas, presence or lack of sulfur, process energy demands, investment cost, availabiUty of solvent, and CO2 recovery requirements. Carbon dioxide is normally recovered for use in the manufacture of urea, in the carbonated beverage industry, or for enhanced oil recovery by miscible flooding. 

Since 1923, methanol has been made commercially from synthesis gas, the route that provides most of the methanol today. The plants are oEten found adjacent to or integrated with ammonia plants for several reasons. The technologies and hardware are similar, and the methanol plant can use the CO2 made in the Haber ammonia process. In this case, the route to methanol is to react the CO2 with methane and steam over a nickel catalyst to give additional CO and H2 and then proceed to combine these to make methanol ... 

Future synthesis questions to be answered in energy integration should include mechanical energy as well as heat energy. For example, the energy conservation schemes required for an ammonia plant require one to consider turbines as well as heat exchangers. 

In this unit significant amounts of Carbon Dioxide get removed fiom the synthesis gas. Usually, Ammonia plants are integrated with Urea production plants to provide the raw material for Urea production (Ammonia CO2) which helps utilize the produced CO2 into usefiil product. However, depending on the capacity of Urea plant, not all of removed CO2 gets used by the Urea plant which leads to releasing excess CO2 to the atmosphere. Estimating how much excess CO2 will be rejected to the atmosphere in this case depends on the Urea production capacity, and it is a case by case estimation. 

Using this process scheme, integrated with an efficient synthesis loop and an efficient steam/power system, net energy consumption as low as 6.50 Gcal/t of ammonia can be obtained for a stand-alone ammonia plant at a cooling water temperature of 30°C (Dybkjaer, 1990). 

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