Ammonia Superheater

Ammonia superheater Heat ammonia vapour to approx. 180°C. 

Ammonia Superheater A shell and tube-type heat exchanger of... 

Ammonia superheater heat-transfer area = 30m2. 

The steam specification stipulates the need for superheated steam at 380°C and 4000 kPa. This medium-pressure product is of sufficient quality for the plant steam-turbine and ammonia superheater, with the remaining portion to be sold to another plant. A heat balance over the entire steam-production circuit concludes that this steam product may be produced at the rate of 5775 kg/h. This result determines the required heat duty for the steam superheater as 585 kW. 

Application -Ammonia superheater Heat-exchange area = 30 m2... 

The ammonia superheater takes the saturated ammonia vapour at 35°C and superheats it to 177°C for mixing with air downstream. Superheated steam at 380°C and 4000 kPa is the heating medium. 

Net heat in from WHB + Heat from ammonia superheater... 

Selection of the high pressure steam conditions is an economic optimisation based on energy savings and equipment costs. Heat recovery iato the high pressure system is usually available from the process ia the secondary reformer and ammonia converter effluents, and the flue gas ia the reformer convection section. Recovery is ia the form of latent, superheat, or high pressure boiler feedwater sensible heat. Low level heat recovery is limited by the operating conditions of the deaerator. 

Superheat is not necessary or desirable for ammonia because the volumetric efficiency is not improved. A few degrees to prevent liquid carry-over are acceptable. The volumetric efficiency can be improved with these typical superheat conditions for R-21 ... 

Example 35.1 An ammonia compressor is rated at 312 kW with saturated suction at -15°C. It is installed with a very long suction line, causing a pressure drop of 0.4 bar, and picks up 6 K superheat from its evaporator condition. Estimate the capacity loss. 

A combined cycle made of two cycles is shown in Fig. 5.2. The upstream topping cycle is a steam Rankine cycle and the downstream bottom cycle is an ammonia Rankine cycle. The following information is provided steam boiler pressure = 2 MPa, steam superheater temperature = 400° C, steam condenser (heat exchanger) pressure = 20 kPa, ammonia boiler (heat exchanger) pressure = 1200 kPa, ammonia condenser pressure = 800 kPa, and mass flow rate of steam = Ikg/sec. 

The major process units include an air compressor to provide feed air to the process, and an ammonia vaporizer and superheater for pretreatment of the feed ammonia. A reactor vessel with a fixed platinum/rhodium catalyst bed quickly oxidizes the ammonia at reaction temperatures approaching 950°C. The reaction yield is 95%. A heat exchanger train immediately following the reactor is used to recover reaction heat. Reaction heat is recovered for both gas expansion (to provide shaft power for the air compressors) and for production of medium-pressure steam (at 380°C and 4000 kPa). The high-level energy available in the process is shared approximately equally between gas expansion and steam production. About 40% of all steam production is delegated to in- house process requirements, leaving about 3200 kg/hour available for export. 

Heat duty to superheat ammonia = FAmm CP (Tout - Tin)... 

The steam production section comprising the steam superheater and waste-heat boiler is designed to lower the reaction-gas temperature from 645°C to 280°C (further oxidation in these vessels will also continue to produce reaction heat). Steam of sufficient quality is to be produced for export to the adjacent ammonia and ammonium nitrate plants. Medium-pressure steam (at 380°C and 4000 kPa) is preferred. 

Synthesis gas is compressed to the synthesis pressure, typically ranging from 140 to 220 kg/cm2g and converted into ammonia in a synthesis loop using radial flow synthesis converters, either the two-bed S-200, the three-bed S-300, or the S-250 concept using an S-200 converter followed by a boiler or steam superheater, and a one-bed S-50 converter. Ammonia product is condensed and separated by refrigeration. This process layout is flexible, and each ammonia plant will be optimized for the local conditions by adjustment of various process parameters. Topsoe supplies all catalysts used in the catalytic process steps for ammonia production. 

Figure 105. Modern integrated single-train ammonia plant based on steam reforming of natural gas (Clide process) a) Sulfur removal b) Primary reformer c) Steam superheater d) Secondary reformer e) Waste heat boiler f) Convection section g) Forced draft fan h) Induced draft fan i) Stack k) TIT and LT shift converters ...

Sorption heat pipe can be used as an efficient multi micro jet cooler of the laser diode with good thermal contact of the SPH porous wick and heat loaded wall, insensitive to some g acceleration and capable to dissipate high heat fluxes q > 200 W/cm for ammonia with low surface superheat. 

The hot gas fiom the incinerator is partially cooled to about 500°F by a heat recovery steam generator. The gas then flows through a de-superheater and a quench vessel. The quench vessel temperature is monitored to ensure that the gas entering the first absorber stage is cool enough to avoid damage to the fiber reinforced plastic absorption vessels. The gas then flows countercurrently through three absorbers where the SO2 is reacted with aqueous ammonia and converted to an aqueous solution of ammonium bisulfite and ammonium sulfite ... 

Vertical vaporizer ( vertical bayonet ) It is widely used for chlorine, ammonia, propane, methanol, sulfur dioxide, etc. Sizes range from 50,000to 15,000,000 Btu/h (12,500 to 3,750,000 kcal/h). Veiy compact, hi productivity, easily combined with built-in superheater with common control. Many heating media can be used, including steam, hot water, and heat transfer fluids such as Dowtherm, Therminol, etc. Electric heated vaporizers also available. Small footprint. (See Fig.V-7.)... 

Ammonia. Vertical vaporizers, often with built-in superheat capability. Normally steel, but sometimes with stainless steel tubes or tubesheets, particularly if the feed material may have trace elements of a corrosive nature. 

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