CO2 removal unit

Fresh reducing gas is generated by reforming natural gas with steam. The natural gas is heated in a recuperator, desulfurized to less than 1 ppm sulfur, mixed with superheated steam, further preheated to 620°C in another recuperator, then reformed in alloy tubes filled with nickel-based catalyst at a temperature of 830°C. The reformed gas is quenched to remove water vapor, mixed with clean recycled top gas from the shaft furnace, reheated to 925°C in an indirect fired heater, and injected into the shaft furnace. For high (above 92%) metallization a CO2 removal unit is added in the top gas recycle line in order to upgrade the quaUty of the recycled top gas and reducing gas. 

CNS-related disorders, sustained drug release for, 9 82-83 CO2. See also Carbon dioxide absorption of, 23 598-599 as an alternative refrigerant, 27 533 removal by alkanolamines, 23 597-600 CO2 emissions, from FCC unit regenerators, 77 720-721 CO2 flooding, in oil recovery, 78 615-617 CO2 removal unit, 70 646, 648 CO2 stimulation, in oil recovery, 78 617 CO-896, chain length and linearity, 2 12t CO-1270, chain length and linearity,... 

Electrical switchyard, 1,200 kVA. Electric boiler, for superheated steam. Water cooling unit (for the CO2 removal unit)... 

Recycle CO2 from the CO2 Removal unit (i.e., the amine unit) is mixed with additional CO2 (that is imported from another process at the Longview Operation) and compressed. Part of the compressed CO2 is exported to another process, and the remainder is heated in the Process Heater. 

The control of the separation section is presented in Figure 3. Because the distillate streams are recycled within the separation section, their composition is less important. Therefore, columns C-3, C-5 and C-6 are operated at constant reflux, while boilup rates are used to control some temperatures in the lower sections of the column. For the absorption columns C-1 and C-4, the flow rates of the absorbent (acetic acid) are kept constant. The concentration of CO2 in the recycle stream is controlled by changing the amount of gas sent to the CO2 removal unit. Temperature and pressure control loops are standard. 

Fresh acetic acid and a liquid acetic acid recycle stream are fed into a vaporizer along with a gas recycle stream and fresh ethylene feed. Oxygen is added after the vaporizer, and reactions occur in a gas-phase reactor. Reactor effluent is cooled and fed into a separator. Vapor from the separator is compressed and fed into an absorber to recover vinyl acetate. Recycle acetic acid is used as lean oil in the absorber. Exit gas from the absorber is sent to a CO2 removal unit, which produces a CO2 purge stream and gas recycle. Another purge stream is used to remove the small amount of ethane that is in the fresh ethylene makeup feed. 

Economics of the process requires high pressure operation and high heat fluxes, which push thermodynamics toward (imdesired) carbon formation. A low SIC ratio will shift the equilibrium of the water gas shift reaction to produce more CO and less CO2 and H2. This will also reduce the size of the CO2 removal unit and CO2 recycle compressor. 

HP steam is used to drive all compressors and heaters, with the utilization of HP steam generated in the process. LP (low pressure) steam generated in the process is utilized in regenerator boilers in Acid Gas Sweetening unit and CO2 Removal unit. 

HYSYS simulation software was used as a tool to complete the simulation of the process (sample is shown in Fig.l). Fluid packages used in the simulation were Amines package which was used for Acid Gas Sweetening and CO2 Removal units, and Peng Robinson which was used for the rest of the units. When simulation was finalized, the following were collected ... 

Flow rates of emitted CO2, kg/hr from Acid Gas Sweetening and CO2 Removal units. 

The simulation of Ammonia process required time and effort to converge with acceptable results. The main parts of simulation that required many trials were the Acid Gas Sweetening and the CO2 Removal units because of the recycle stream material balance and the required purity of gas streams. Absorbers and distillation columns are usually sensitive to composition and flow rates (L. Oi, 2007 I. Halim and R. Srinivasan,... 

As Fig.2 and Table 1 show, increasing the flow rate of Ammonia produced by 66.6% resulted in a decrease in total plant Carbon Footprint (= 2.8 - 6.6%) considering all scenarios. Carbon Footprint of each unit increased with increased production rate except for the Ammonia Synthesis loop where this decrease occurred. A total decrease of ( 3.8 - 6%) of plant Carbon Footprint occurred when using sweet gas instead of sour gas that has to be treated first. Moreover, the utilization of HP and LP steam reduces the overall Carbon Footprint (= 12.5 - 15%). LP steam is utilized in boilers of coliimns in both Acid Gas Sweetening and CO2 Removal units. 

Although Ammonia production process is claimed to be clean compared to other processes, the estimated Carbon Footprint of Ammonia process considering process emissions and major utility emissions range between 785 and 999 kg C02/ton Ammonia depending on production rate, type of feedstock, and steam utilization. The use of HYSYS simulation tool with MS Excel was very useful to estimate these values. Further improvements on the simulation especially for CO2 Removal unit are required to get more accurate results consistent with desired CO2 recovery. These improvements can help in proposing new modifications on the process to reduce energy consumption and hence CO2 emissions. 

Upgrading the CO2 removal unit would minimize hydrogen loss in the Methanator, resulting in a potential capacity increase. 

As in the Braun process, the size of the primary reformer is reduced and the size of the air compressor increased in the AMV process compared to more conventional process schemes. This is due to the operation with excess process air and with high methane leakage. Power consumption in the synthetic gas compressor is low because of the low synthesis pressure and the low suction temperature (gas direct from the low temperature Selexol CO2 removal unit), but this is compensated by increased power consumption for the compression of excess nitrogen and high power consumption in the refrigeration section. 

Since the quantity of CO2 dissolved in oil varies over a large range of values during the whole production of the reservoir (levels from 40% up to 90% can be observed after a few years of production),it is rather difficult to design a cost-effective CO2 removal unit that could operate during the entire life of the reservoir. Therefore, modular CO2 removal units such as membrane operations offer much flexibility for such an operation (Table 6.3). 

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