3.2 Post Combustion Capture Plant

3.2.1 Description of 5000tpd Post Combustion Capture Plant

The PCC technology IP proprietor’s (MHI) flue gas CO2 capture plant utilizes an advanced hindered amine solvent, as the CO2 absorbent. During the development of this project it was agreed with Global CCS Institute and the PCC technology proprietor to use a standard 5000tpd PCC plant which would be provided with flue gas from one Loy Yang A boiler plant. This 5000tpd PCC plant is rated to capture 90% of the feed flue gas (i.e. 90% efficient).

3.2.2 Technical Process Description for the 5000tpd PCC Plant

The process for the 5000tpd plant consists of three main sections described below: (1) Flue gas pretreatment section, (2) CO2 capture section, (3) CO2 Compression and Dehydration section. A block flow diagram illustrating these sections and brief descriptions of each section are as follows in Figure 3.3.

Figure 3.3 -Block Flow Diagram of PCC Plant

Source: MHI

(1) Flue Gas Pre-treatment Section

SO2 absorber

The SO2 absorber consists of a single tower complete with oxidation equipment and single spray pipes. Flue gas is introduced into the SO2 absorber where it makes contact with limestone slurry. SO2 contained within flue gas is absorbed and oxidized to form gypsum during this process.

Deep FGD section

The flue gas enters the integrated deep FGD section in the bottom part of the Flue gas quencher, where the flue gas contacts directly with an alkaline, pH controlled solution to remove SO2,

Flue gas washing section

After passing the deep FGD section, the flue gas moves upward into the flue gas washing section through packing. At this stage the temperature of the flue gas from the deep FGD is too high to feed directly into the CO2 absorber since a lower temperature for exothermic reaction of CO2 molecules and solvent is preferred. Therefore, prior to entering the CO2 absorber, flue gas is cooled in the flue gas quencher by direct contact with circulating water supplied from the top the quencher.

(2) CO2 Capture Section

CO2 absorption

The CO2 absorber also uses packing. It consists of two main sections, (1) the CO2 absorption section in the lower part and (2) a water wash section in the upper part.

  1. CO2 absorption sectionThe pre-treated flue gas from the flue gas quencher is introduced into the bottom section of the CO2 absorber. The flue gas moves upward through packing material, while lean solvent is introduced from the top of the absorption section directly onto the packing. The flue gas spreads evenly within the packing, before coming in contact with the solvent on the surface of the packing, where the CO2 in the flue gas is selectively absorbed by the solvent.The rich solvent from the bottom of the CO2 absorber is pumped by the rich solution pump and then is directed to the regenerator via the solution heat exchanger.
  2. Water wash sectionThe flue gas from the CO2 absorption section moves upward into the water wash section into the upper part of CO2 absorber. The treated gas is washed by water, thus removing any vaporized solvent and is cooled down to maintain the water balance within the system. The water wash section features a combination of packing and several demisters. One special proprietary demister which is specifically developed by MHI is included in this system. The system configuration of MHI’s proprietary design has been commercially demonstrated in several plants throughout the world.

Solvent regeneration

Regeneration takes place in a cylindrical column using packing where the rich solvent is steam-stripped, using low pressure steam, to remove CO2.

The rich solvent from the bottom of the CO2 absorber is heated by the lean solvent from the bottom of the regenerator by means of a solution heat exchanger. The heated rich solvent is then introduced into the upper section of the regenerator, where it contacts with the stripping steam over the packing.

The steam in the regenerator is produced by the regenerator re-boiler which uses LP steam to boil the lean solvent. The condensate from the regenerator re-boiler is collected in the steam condensate drum and then pumped to the battery limit by the steam condensate return pump. The overhead vapour leaving the regenerator column is cooled by the regenerator condenser and condensate water is collected in the regenerator reflux drum.

The lean solvent is cooled to an optimum reaction temperature by the solution heat exchanger and lean solution cooler prior to being sent to the CO2 absorber. Some of the solvent flow is filtered to remove oil and soluble impurities which is likely to be contaminants arising from the flue gas stream.

(3) CO2 compression & Dehydration section

Product CO2 gas is sent to the CO2 compression and dehydrated section, where after passing through the low pressure stage of the CO2 compressor, it is sent to the dehydration plant in order to dehydrate product CO2. The CO2 compressor will compress product CO2 to a pressure of 100 bar before being transferred to pipeline where it will be sent to the sequestration site.

3.2.2.1 SOLVENT RECLAIMING (INTERMITTENT OPERATION)

The primary purpose of the reclaiming is to remove soluble solvent degradation products such as heat stable salts (HSS) from the solvent. The Reclaimer operates as a simple batch distiller, and since the solvent degradation products and the salt have higher boiling temperatures than water or solvent, they remain in the reclaimer kettle where they can easily be collected for disposal.

3.2.2.2 UTILITY

Steam system

LP steam is required for the operation of the PCC plant. The LP steam is used to boil lean solvent through regenerator re-boiler. The PCC plant base case for driving the CO2 compressor is by an electric motor.

On an intermittent basis, MP steam is used to boil solvent during reclaiming operations.

Condensate is collected in a condensate drum which will be sent back to the station’s condensate system.

3.2.3 PCC Plant Dry Air Cooling System

The dry air cooling system of the PCC plant (used for Case 5) is proposed to be configured based on a closed cooling water circulation system equipped with air cooled heat exchangers.

This differs from the conventionally configured wet type open loop cooling water systems (e.g. once through or wet cooling tower systems).

For Case 5, the air cooling system will replace the wet cooling system of the PCC plant that is used for the following heat loads:

  • Flue Gas Cooling Water Cooler
  • Wash Water Cooler
  • Lean Solution Cooler
  • Absorption Intermediate Cooler
  • Regenerator Condenser
  • 1st Stage to 6th Stage Discharge Coolers
  • Low/High Pressure Stage CO2 Compressor Stage Cooler