Capture Technology For Ngcc Power Plant Engineering Essay

Typically, there are three chief C gaining control engineerings, oxy-fuel burning gaining control, pre-combustion gaining control and post-combustion gaining control. All these three techniques can be used in NGCC power works to capture CO2. Adding CO2 gaining control system into a NGCC power works would take to net efficiency punishment, shows in figure 1.

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Figure1. Efficiency of different gaining control options with regard to NGCC without gaining control ( Kanniche M. , 2010 )

Harmonizing to Figure 1, the net efficiency of NGCC works without gaining control is the highest, about 60 % . For CO2 gaining control system consumes power, net efficiencies of workss with different gaining control method bead in assorted grades. Post-combustion gaining control NGCC works ‘s figure is approximately 50 % , and the efficiency of oxy-fuel NGCC is about 48 % . Pre-combustion gaining control NGCC works ‘s efficiency is the lowest, approximately 45 % .

Another factor demand to be considered is the investing. As Figure 2 shows, pre-combustion gaining control is most expensive, and following is oxy-fuel method. Post-combustion is the lowest 1.

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Figure2. Investing cost for different gaining control options with regard to NGCC without gaining control ( Kanniche M. , 2010 )

Based on all above treatment, a sensible decision could be made is that post-combustion gaining control is the best pick for NGCC power works.

Case 4 NGCC+ CCS + Coal Ready

Description of CCPP

Combined rhythm unit is chiefly made up by gas turbine, waste heat boiler and steam turbine. Among these three constituents, gas turbine plays the cardinal function. The proficient characteristics of gas turbine affect the combined efficiency. Gas turbine and its auxiliaryA equipment signifier Gas System for CCPP. Beyond this, waste heat boiler and steam turbine constitute the Steam System. Parameters in Steam System are chiefly affected by exhaust parametric quantities of gas turbine, and the public presentation of Steam System would be near linked to exhaust parametric quantities of gas turbine as good.

This design is for a 1600 MW power works, dwelling of two indistinguishable trains of natural gas fired, standard combined rhythm units. Each of the two combined rhythm bundles comprises:

two Siemens gas turbines ( SGTA® ) : SGT5-4000F

a Siemens steam turbine ( SSTA® ) : SST5-5000

a triple-pressure reheat heat recovery steam generator ( HRSG ) with BENSON HP evaporator

The gas turbines and steam turbine for each unit are connected to their ain air- cooled generator.

Gas Turbine Description

Gas turbine is the most of import unit in combined rhythm power works. The proficient characteristics of gas turbine affect the combined efficiency. Gas turbine and its auxiliaryA equipment signifier Gas System for CCPP. In this design, Siemens Gas Turbine, SGT5-4000F is chosen.

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Figure3. Siemens SGT5-4000F Gas Turbine Performance Data ( Siemens, 2008 )

As Figure 3 shows, the gross power end product of this gas turbine is 292MW, and the gross efficiency is 39.8 % . These public presentations are good fundamental for combined rhythm unit. Each bundle has two gas turbines like this, therefore the Gas System end product should be 584 MW.

Heat Recovery Steam Generator ( HRSG ) Description

Waste heat boiler is another of import constituent in combined rhythm unit. In the boiler, H2O heat exchange with flow gas, bring forthing different force per unit area steams to drive the steam turbine.

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Figure4. Mechanism of Heat Recovery Steam Generator ( HRSG )

Figure 4 shows HRSG. Typically, in waste heat boilers, flue gas from gas turbine moves horizontally, and H2O moves in perpendicular tubing interchanging heat with the fumes gas flow. The force per unit area and temperature of steams are based on steam turbine demands.

Steam Turbine Description

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Figure5. View of the internal of a typical power station steam turbine ( Doosan, 2011 )

The steam turbine is divided into the undermentioned subdivisions:

HP subdivision, which is drive by steam from the HP super warmer

MP subdivision, which is drive by a mixture of steam from the MP super warmer and steam from the HP turbine

LP subdivision, which is drive by a mixture of steam from the LP super warmer and steam from the IP turbine subdivision

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Figure6. Siemens SST5-5000 Steam Turbine Performance Data ( Siemens, 2008 )

Figure 5 shows the proficient public presentation of the chosen steam turbine. In combined rhythm applications, the end product scope is from 120MW to 500MW. In this design, one bundle should provide 800MW power, and gas turbines have supplied 584MW already. Therefore, this steam turbine could run into the basic demand and has some trim capacity to set the excess demand.

Findingss and Discussion

After taking chief constituents of CCPP, the concluding public presentation of combined rhythm bundle shows in Figure 7.

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Figure7. Performance of CCPP ( Siemens, 2008 )

The layout of this design is Multiple-Shaft. “ When power works runs at 100 % of its burden, multiple-shaft power works has a higher net efficiency than individual power works ‘s, approximately 0.5 % higher. When power programs run at 50 % ~ 100 % of its burden, the net efficiencies are basic same. However, when power workss run at 50 % of its burden, individual shaft efficiency is a small higher than that in multiple shaft. When power workss have to run at a degree below 50 % of their tonss, individual shaft is better than multiple one ” ( Zhu, 2002 ) .

Another disadvantage of multiple-shaft power works is the operation flexibleness. In this design, power works merely has two big capacity combined rhythm bundles, when the equipment needs fix, power works end product is difficult to keep.

Based on what mentioned supra, this design has a possible to better, for illustration, utilizing several little burden individual shaft combined rhythm bundles replace the two trains of large bundles.

Capture Plant

The Capture Plant absorbs CO2 from the fumes gas which is from the CCPP. After interchanging heat with H2O and bring forthing different force per unit area steams, the fumes gas is foremost cooled in a H2O quench and most of the steam in the fluke gas is condensed at that place. Then, the cooled fumes gas is delivered to the CO2 absorber where CO2 is absorbed by absorbent. Following, the CO2 thin fluke gas could be emitted. The rich absorbing solution is regenerated through heating with steam, and the captured C dioxide is compressed and dried for conveyance.

Quench Unit

After interchanging heat with H2O and bring forthing different force per unit area steams, the gas turbine fumes is still excessively hot, and it contains excessively much steam to be fed straight to the CO2 absorber. The quench column is used to chill the exhaust watercourse to approach ambient and condenses most of the steam.

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Figure8. Schematic flow of Quench Column

The quench column is a big packed tower where a big sum of H2O which moves up to down in it. The gas turbine fumes moves up and is cooled by direct contact chilling. A big volume of go arounding H2O is required to chill the fumes gas to take the important and latent heat.

The H2O from the underside of the quench column is cooled through contacted with sea H2O in money changers and returned to the top of the quench column. The excess H2O from condensed steam, is sent to blow H2O intervention.

The cooled fluke gas leaves the top of the quench column and so delivered to the CO2 absorber.

CO2 remotion procedure

There have two chief types of absorbent for CO2 ; chemical dissolvers like aminoalkanes and physical dissolvers such as poly ethanediol.

For post-combustion, the CO2 concentration in flue gas from turbine is particularly low because big volumes of un-combusted air are used for fluxing intents: foremost, cool burning fires ; 2nd, command the recess temperature of turbine ; 3rd, cool stator and rotor blades.

“ The typical CO2 content of gas turbine fumes is 3-4 % by volume, which compares starkly with a typical figure of 10-15 % for discharged boilers. ( IEAGHG, 2005 ) ” This means that efficiency of soaking up is low and requires big volumes of dissolver. Meanwhile, the low concentration of CO2 in the fluke gas besides means that it is really difficult for solution regeneration by simple force per unit area decrease. Therefore, regeneration has to devour excess energy, which could be achieved by depriving the rich dissolver with steam. The steam is normally generated by merely boiling portion of the H2O in the solution. The big volumes of solution and the absence of any advantage from force per unit area flash mean that heating burden is really high. This leads to the chief job of post-combustion gaining control — — punishment of net efficiency from steam turbine.

Based on all discussed above, a determination could be made is that chemical dissolvers are better than physical dissolvers for they have a stronger affinity for the CO2 and hence less dissolver could be used.

Typically, chemical dissolvers used in CO2 gaining control can split into following subdivisions:

Amine-based dissolvers ( MEA, DEA, TEA, MDEA and so on )

Ammonia

At high force per unit area, ammonium hydroxide may organize explosive substances, therefore it is non widely used in CO2 remotion. Compared with ammonium hydroxide, because of their high efficiency and easy operation, amine-based dissolvers are widely used in industries.

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Figure9. Comparison of different amine-based dissolvers ( Supitcha Rinprasertmeechai, 2012 )

As Figure 9 shows, MEA has the highest capacity of CO2 soaking up in aminoalkane based dissolver.

Except dissolver shows in Figure 9, there is another competitory option, MDEA. Compared with MEA, MEDA is better when operated at a high CO2 concentration, and the environment in this instance is an oxidising environment which is non good for MDEA.

The mechanism of CO2 separation shows in Figure 10. CO2 is removed from the cooled fluke gas by scouring with MEA. The fluke gas is delivered to the underside of the absorber. It flows up the jammed column contacts with a down fluxing solution of MEA. The down fluxing solution is “ thin ” in CO2 content. During the contact, CO2 is absorbed from the fluke gas and doing a “ rich ” solution, which leaves the underside of the absorber. The fluke gas, after holding a full contact with MEA, is thin in CO2 content, which emits from stack.

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Figure10. CO2 soaking up and desorption ( CO2CRC, 2011 )

The captive CO2 is desorbed from the rich solution in the desorber. The rich solution is pumped from the underside of the absorber and so heated in the rich/lean money changer. The hot rich solution moves to the top of the desorber and flows down, contacted with an up flow of steam which desorbs CO2 from the solution. The steam is generated in the desorber reboiler from the H2O in the amine solution and the heat for the reboiler is supplied by low force per unit area steam from the CCPP HRSG. This is the root cause of power works end product punishment.

Findingss and Discussion

The gaining control works comprises flue gas scouring with an MEA solution. The solution is regenerated in a reboiled sdesorber with the heat supplied by low-pressure steam taken from the steam rhythm of the CCPP.

Coal Ready Plant

The intent of coal ready is to derive the fuel flexibleness of power workss. Due to the uncertainness of energy market, it is necessary to see fuel retrofit for natural gas combined rhythm power works. The chief differences between coal-burning CCPP and gas-fired CCPP are natural stuff pretreatment and gaining control engineering.

CO2 gaining control is changed for taking the C from the coal before burning. The Capture Plant converts the coal by gasification to synthesis gas, which is a mixture of CO and H2. After gaining control of CO2 the carbon-free syngas is fed to the gas turbine.

Capture Plant Description

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Figure11. Pre-combustion Capture Plant ( COSTAIN, 2008 )

The gaining control works converts coal to a syngas mixture of H2 and N2 suited for a gas turbine. The works consists of a gasification phase where a mixture of coal and H2O is gasified with O2 from an air separation unit ( ASU ) . Then, the syngas which is a mixture of H2, CO2, CO and N2 is fed to a CO displacement reactor, where the CO and steam are reacted to H2 and CO2. In following phase, utilizing a physical dissolver, H2S is removed from the shifted syngas. Then, CO2 is removed every bit good through the same engineering in NGCC mentioned supra. Finally, the syngas changes its force per unit area to a suited figure for gas turbine.

Potential for Retrofit

As Figure 11 shows, for coal ready NGCC power works, a serious of excess equipment is needed to change over coal to fuel gas. In the design stage, several jobs should be taken into history, as shown below:

Space for Coal Storage

Space for Air Separation Unit

Space for Gasifier

Space for Particle Remover

Space for CO Shift Reactor

Space for Sulphur Remover

Space for Ash Storage

Based on all facets mentioned above, for coal ready works in this design, infinite modesty needs to be taken into history.

Findingss and Discussion

As it shows above, coal retrofit for a natural gas fired power workss needs wholly different procedure and extra equipment. Therefore, in this period, this proposal is excessively expensive and merely provinces at ready for retrofit.

Fiscal Appraisal