Capital Cost

 

This is a standard capital cost result screen. The amine system in PC and NGCC plants has the following process areas:

•SO2 Polisher/Direct Contact Cooler (PC) or Direct Contact Cooler (NGCC): This area includes the equipment required to cool the flue gas in order to improve absorption of CO2 into the amine sorbent. For PC plants, an SO2 polisher may be used to reduce the SO2 concentration to very low levels. For all plant types, a direct contact cooler is typically used in plant configurations that do not include a wet FGD. A direct contact cooler is a large vessel where the incoming hot flue gas is placed in contact with cooling water. The cost is a function of the gas flow rate and temperature of the flue gas. In case of coal-fired power plant applications that have a wet FGD (flue gas desulfurization) unit upstream of the amine system, the wet scrubber helps in substantial cooling of the flue gases, and additional cooler may not be required.

•Flue Gas Blower: The flue gas has to overcome a substantial pressure drop as it passes through a very tall absorber column, countercurrent to the sorbent flow. Hence the cooled flue gas has to be pressurized using a blower before it enters the absorber.

•CO2 Absorber Vessel: This is the vessel where the flue gas is made to contact with the MEA-based sorbent, and some of the CO2 from the flue gas gets dissolved in the sorbent. The column may be plate-type or a packed one. Most of the CO2 absorbers are packed columns using some kind of polymer-based packing to provide large interfacial area.

•Heat Exchangers: The CO2-loaded sorbent needs to be heated in order to strip off CO2 and regenerate the sorbent. On the other hand, the regenerated (lean) sorbent coming out of the regenerator has to be cooled down before it can be circulated back to the absorber column. Hence these two sorbent streams are passed through a cross heat exchanger, where the rich (CO2-loaded) sorbent gets heated and the lean (regenerated) sorbent gets cooled.

•Circulation Pumps: The cost associated with the equipment required to support FGD system operation such as makeup water and instrument air are treated here.

•Sorbent Regenerator: This is the column where the weak intermediate compound (carbamate) formed between the MEA-based sorbent and dissolved CO2 is broken down with the application of heat and CO2 gets separated from the sorbent to leave reusable sorbent behind. In case of unhindered amines like MEA, the carbamate formed is stable and it takes large amount of energy to dissociate. It also consists of a flash separator where CO2 is separated from most of the moisture and evaporated sorbent, to give a fairly rich CO2 stream.

•Reboiler: The regenerator is connected with a reboiler which is basically a heat exchanger where low-pressure steam extracted from the power plant is used to heat the loaded sorbent.

•Steam Extractor: In case of coal-fired power plants that generate electricity in a steam turbine, a part of the LP/IP steam has to be diverted to the reboiler for sorbent regeneration. Steam extractors are installed to take out steam from the steam turbines.

•Sorbent Reclaimer: Presence of acid gas impurities (SO2, SO3, NO2 and HCl) in the flue gas leads to formation of heat stable salts in the sorbent stream, which cannot be dissociated even on application of heat. In order to avoid accumulation of these salts in the sorbent stream and to recover some of this lost MEA sorbent, a part of the sorbent stream is periodically distilled in this vessel. Addition of caustic helps in freeing of some of the MEA. The recovered MEA is taken back to the sorbent stream while the bottom sludge (reclaimer waste) is sent for proper disposal.

•Sorbent Processing: The regenerated sorbent has to be further cooled down even after passing through the rich/lean cross heat exchanger using a cooler, so that the sorbent temperature is brought back to acceptable level (about 40 deg C). Also, in order to make up for the sorbent losses, a small quantity of fresh MEA sorbent has to be added to the sorbent stream. So, the sorbent processing area primarily consists of sorbent cooler, MEA storage tank, and a mixer. It also consists of an activated carbon bed filter that adsorbs impurities (degradation products of MEA) from the sorbent stream.

•Drying and Compression Unit: The CO2 product may have to be carried very long distances via pipelines. Hence it is desirable that it does not contain any moisture in order to avoid corrosion in the pipelines. Also, it has to be compressed to very high pressures so that it gets liquefied and can overcome the pressure losses during the pipeline transport. The multi-stage compression unit with inter-stage cooling and drying yields a final CO2 product at the specified pressure (about 2000 psig) that contains moisture and other impurities (e.g., N2) at acceptable levels.

•Auxiliary Natural Gas Boiler: The cost of the natural gas boiler is estimated on the basis of the steam flow rate generated from the auxiliary boiler.

•Auxiliary Steam Turbine: The regeneration heat is provided in the form of low pressure (LP) steam extracted from the steam turbine (in case of coal-fired power plants and combined-cycle gas plants), through the reboiler (a heat exchanger). In case of simple cycle natural gas fired power plants, a heat recovery unit maybe required.

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