NH3 plant

Synthesis-Gas-Production Processes. These processes were improved and developed as a result of changes in feedstock availability and economics. Before World War II, most NH3 plants obtained H2 by reacting coal or coke with steam in the water-gas process, A small number of plants... 

Power Recovery in Other Systems. Steam is by far the biggest opportunity for power recovery from pressure letdown, but others such as tailgas expanders in nitric acid plants (Fig. 1) and on catalytic crackers, also exist. An example of power recovery in liquid systems, is the letdown of the high pressure, rich absorbent used for H S/C02 removal in NH3 plants. Letdown can occur in a turbine directly coupled to the pump used to boost the lean absorbent back to the absorber pressure. 

Figure 5. Relative NH3 plant investment vs. feedstock (1150 STPD)...

In plants nitrate is reduced to nitrite in the cytoplasm after which the nitrite is reduced to NH3 in the chloroplasts (Galbally 1989). Consequently, plants emit NO and NH3. Plants also take up NH3 and NO2 very rapidly. This NO2 is chemically produced by atmospheric oxidation of biogenic and anthropogenic emitted NO, either above the canopy, or below the canopy from soil-emitted NO. In the last... 

Used as a sii e-st e or two-stage system. Used in NH3 plants up to 1,360 tpd capadty. Commercialized recent in a l,640 qxl and a 472-tpd ammcHTia plant prewDusty udng conventional K2CO3 processes (57). 

Figure 6.1.9 shows a flow sheet of an NH3 plant without syngas production. In Section 6.2, a plant based on natural gas is shown (Figure 6.2.3), but here we only consider NH3 synthesis. 

Figure 6.1.9 Flow sheet of an ammonia synthesis plant (H1-H5 heat exchangers, Cl compressor for fresh syngas, C2 recycle compressor). Adapted from Baerns et al. (2006). For syngas formation and an overview of a complete NH3 plant see Section 6.2 (Figure 6.2.3).

Figure 6.2.3 Block diagram and temperature profile for a steam refoming NH3 plant. Adapted from AppI (1999).

Ammonia formation is lessened due to the fact that the residence time of the steam methane reformer is designed for hydrogen production not ammonia production with recycle. In an NH3 plant, the ammonia is considered to be at equilibrium in a secondary reformer that is operating approximately 300°F to 500°F higher than a traditional steam methane reformer. Therefore for calculations, the worst case for ammonia production in a hydrogen plant can be assumed to be equilibrium at the reformer outlet temperature plus an additional 300°F. 

Catacarb Process Design Summary for CO2 Removal In a 1000 Std.T/Day NH3 Plant... 

The short-term exposure of humans, animals, and plants to gaseous pollutants is more severe than that for pollutants in other matrices. Since the composition of atmospheric gases can show a substantial variation over a time, the continuous monitoring of atmospheric gases such as O3, CO, SO2, NH3, H2O2, and NO2 by in situ sampling is important. 

These reactions can be limited or prevented by proper plant design, coiTcct mixing of the burner gas, and keeping the catalyst activity high. Modern plants convert about 97% of NH3 to NO. 

Nitrous gases originating from the combustion units in nitric acid plants carry small amounts of unreacted ammonia, NH3. The ammonia may react with the nitrous gas to form microscopic particles of ammonium nitrate that adhere to solid surfaces. Within a short time, there is a growing layer of ammonium nitrate salt covering the internal surface of the nitrous gas compressor (Figure 4-27). This layer can obstruct the flow passages because it tends to increase the power consumption, provoke excessive vibrations, and even present a safety hazard since ammonium nitrate explosions can occur. 

World production of synthetic ammoma hos increased dramatically particularly during the period 1950-80. Production in 1950 was Mule more ihan 1 million tonnes, thou this was huge when compared with the production of most o r compounds, it is dwarfed by today s rale of production which exceeds 120 million tonnes pa. In 1990 world production capacity was 119.6 million tunoes distributed os follows Asia 35.4%, the former Soviet Umon 21,5%. North America 13 8%, Western Europe 11.3%, Ea rem Europe 9.7% Latin America 5.3%, Africa 30%. The price of NH3 (FOB Gulf Coast plants, USA) was l07/tonne in 1990. 

The modem process for manufacturing nitric acid depends on the catalytic oxidation of NH3 over heated Pt to give NO in preference to other thermodynamically more favour products (p. 423). The reaction was first systematically studied in 1901 by W. Ostwald (Nobel Prize 1909) and by 1908 a commercial plant near Bochum. Germany, was producing 3 tonnes/day. However, significant expansion in production depended on the economical availability of synthetic ammonia by the Haber-Bosch process (p. 421). The reactions occurring, and the enthalpy changes per mole of N atoms at 25 C are ... 

A wet environment exists in the FCC gas plant. Water comes from the condensation of process steam in the main fractionator overhead condensers. In the presence of H S, NH3, and HCN, this environment is conducive to corrosion attacks. The corrosion attack can be any or all of the following types [2] ... 

Besides nitrogen fixation, the only other major source of reduced nitrogen is the decomposition of soil or aquatic organic matter. This process is called ammonification. Heterotrophic bacteria are principally responsible for this. These organisms utilize organic compounds from dead plant or animal matter as a carbon source, and leave behind NH3 and NHJ, which can then be recycled by the biosphere. In some instances heterotrophic bacteria may incorporate a complete organic molecule into their own biomass. The majority of the NH3 produced in this way stays within the biosphere however, a small portion of it will be volatilized. In addition to this source, the breakdown of animal excreta also contributes to atmospheric... 

Many malodorous compoimds are not only nuisance, but also a health threat under prolonged exposure [1]. Ammonia (NH3) is emitted from landfill and sewage treatment plant and associated with many agricultural activities (e.g. poultry and piggery). Ammonia is also a problem in public toilets, hospitals and nursing homes. Selective eatalytie oxidation (SCO) can convert NH3 to N2 at mild temperature (i.e. 473-673 K) as shown in equation 1, however nitrous oxides (N2O) and nitrogen oxides (NOj) are often produced cf. Eqn. 2 3). 

The vanadium content of some fuels presents an interesting problem. When the vanadium leaves the burner it may condense on the surface of the heat exchanger in the power plant. As vanadia is a good catalyst for oxidizing SO2 this reaction may occur prior to the SCR reactor. This is clearly seen in Fig. 10.13, which shows SO2 conversion by wall deposits in a power plant that has used vanadium-containing Orimulsion as a fuel. The presence of potassium actually increases this premature oxidation of SO2. The problem arises when ammonia is added, since SO3 and NH3 react to form ammonium sulfate, which condenses and gives rise to deposits that block the monoliths. Note that ammonium sulfate formation also becomes a problem when ammonia slips through the SCR reactor and reacts downstream with SO3. 

In the area of pollution control, file removal of NOx from stationary sources effluents, such as power plant stack gases, has been accomplished by use of titania-vanadia catal)rsts, which promote the reduction of NOx with NH3 to produce nitrogen and water. 

Alkali-promoted Ru-based catalysts are expected to become the second generation NHs synthesis catalysts [1]. In 1992 the 600 ton/day Ocelot Ammonia Plant started to produce NH3 with promoted Ru catalysts supported on carbon based on the Kellogg Advanced Ammonia Process (KAAP) [2]. The Ru-based catalysts permit milder operating conditions compared with the magnetite-based systems, such as low synthesis pressure (70 -105 bars compared with 150 - 300 bars) and lower synthesis temperatures, while maintaining higher conversion than a conventional system [3]. 

Example 25.5 A gas turbine exhaust is currently operating with a flowrate of 41.6 kg s-1 and a temperature of 180°C after a heat recovery steam generator. The exhaust contains 200 ppmv NOx to be reduced to 60 rng rn 3 (expressed as N02) at 0°C and 1 atm. The NOx is to be treated in the exhaust using low temperature selective catalytic reduction. Ammonia slippage must be restricted to be less than 10 mgm 3, but a design basis of 5 mg-rn 3 will be taken. Aqueous ammonia is to be used at a cost of 300 -1 1 (dry NH3 basis). Estimate the cost of ammonia if the plant operates... 

A wide range of catalytic materials have been investigated for the selective catalytic reduction of NOx. For stationary emissions, NH3-SCR using vanadium-tungsten oxides supported on titania is the most used method however, when there is a simultaneous emission of NO and NOz (in tail gas from nitric acid plants), copper-based zeolites or analogous systems have been proven to be preferable [31b], In fact, there are two main reactions for NH3-SCR ... 

We may thus conclude after this short overview on DeNO technologies that NH3-SCR using catalysts based on V-W-oxides supported on titania is a well-established technique for stationary sources of power plants and incinerators, while for other relevant sources of NO, such as nitric acid tail gases, where emissions are characterized from a lower temperature and the presence of large amounts of NOz, alternative catalysts based on transition metal containing microporous materials are possible. Also, for the combined DeNO -deSO, alternative catalysts would be necessary, because they should operate in the presence of large amounts of SO,.. Similarly, there is a need to develop new/improved catalysts for the elimination of NO in FCC emissions, again due to the different characteristics of the feed with respect to emissions from power plants. 

NO, which consists primarily of NO with less amounts of N02 in power plant emissions, is converted to N2 by reaction with NH3 over the catalyst in the presence of oxygen (Eqn. 3). A small fraction of the S02, produced in the boiler by oxidation... 

---