THERMODYNAMIC PERFORMANCE EVALUATION …...cycle) and bottoming (simple cycle) cycles for small to medium biomass plant as alternative to reciprocating IC or organic Rankine cycle

1111thth European Conference on Coal Research and its ApplicationEuropean Conference on Coal Research and its Application

(ECCRIA 11)(ECCRIA 11)

THERMODYNAMIC PERFORMANCE EVALUATION OFTHERMODYNAMIC PERFORMANCE EVALUATION OF

(ECCRIA 11)(ECCRIA 11)

THERMODYNAMIC PERFORMANCE EVALUATION OF THERMODYNAMIC PERFORMANCE EVALUATION OF SUPERCRITICAL COSUPERCRITICAL CO22 CLOSED BRAYTON CYCLES CLOSED BRAYTON CYCLES

FOR COALFOR COAL--FIRED POWER GENERATION WITH POSTFIRED POWER GENERATION WITH POST--COMBUSTION CARBON CAPTURECOMBUSTION CARBON CAPTURE

Olumide Olumayegun, Meihong Wang, Eni Oko

Process and Energy Systems Engineering GroupUniversity of Hully

OutlineOutlineOutlineOutline

Background & Motivation

Contributions of StudyContributions of Study

Process Configurations and Description

Steady State Modelling in Aspen Plus

Results and Discussions

ConclusionsConclusions

Acknowledgement

05/09/201611th European Conference on Coal Research and its Applications, University of Sheffield, Sheffield, UK 2

Background & MotivationBackground & MotivationBackground & MotivationBackground & Motivation Coal-fired power plants are still playing significant role inCoal fired power plants are still playing significant role in

meeting world energy demands However, electricity generation from coal-fired power

plants constitute the largest source of CO2 emissions In the UK, emissions from electricity generation account

f d t f th UK t t lfor around a quarter of the UK total

D t S DECC 2015

3

Data Source: DECC, 2015

05/09/201611th European Conference on Coal Research and its Applications, University of Sheffield, Sheffield, UK

Background & MotivationBackground & MotivationBackground & MotivationBackground & MotivationCoal-fired Power Generation with Post-combustion CO2 Capture2 p

Steam PowerS-CO2 Closed

39% efficiency42% efficiency

Power PlantBrayton Cycle

Coal Fuel

Coal+AirCombustion

CO2Capture

Efficiency improvement

CO2 capture

Possible l f

Options for CO2 emission reduction from power plant

replacement of steam cycle with s-CO2 cycle

4

p p


Background & MotivationBackground & MotivationBackground & MotivationBackground & MotivationSupercritical CO2 Closed Brayton Cycle Power PlantSupercritical CO2 Closed Brayton Cycle Power Plant Supercritical steam cycles represent the state-of-the-art in coal-

fired power generationS iti l t l t i ffi i b d Supercritical steam power plant increases efficiency based on an increase in main steam conditions (supercritical pressure & high TIT)

ff However, achievable efficiency improvement is limited by material technology

S-CO2 cycle is promising for further efficiency improvement at 2 y p g y pcurrent conditions of pressure and temperature

Other advantages: Simpler than steam cycle, smaller footprint, applicable to other energy sources (nuclear, solar, geothermal, pp gy ( , , g ,waste heat)


Contributions of StudyContributions of StudyContributions of StudyContributions of StudyS-CO2 cycle for coal, biomass and bottoming cycle applications in 2 y , g y ppliterature Manente and Lazzaretto (2014): S-CO2 Brayton cycles comprising topping (recompression

cycle) and bottoming (simple cycle) cycles for small to medium biomass plant as alternative to reciprocating IC or organic Rankine cycle engines◦ Efficiency 10%-point higher than existing biomass power plant

Le Moullec (2013): Conceptual study and design of coal-fired power plant built around a S-CO2 power cycle and 90% post-combustion CO2 capture◦ Double reheat (3 turbines), 3 recuperatorsoub e e eat (3 tu b es), 3 ecupe ato s◦ Improve heat energy utilisation by cold CO2 bleeding from two locations and 2 stages of

combustion air preheating◦ 15% reduction in levelised cost of electricity and 45% reduction in cost of avoided CO2

Mecheri and Le Moullec (2016): Investigates coal-fired S-CO2 cycle from thermodynamicMecheri and Le Moullec (2016): Investigates coal fired S CO2 cycle from thermodynamic consideration by comparing effects of number of reheat, number of recompression and advanced flue gas economiser configurations◦ Improve heat energy utilisation by transferring flue gas heat to a fraction of cold CO2 and

preheating secondary air until 510 0C ◦ The plant net efficiency is higher than supercritical and ultra-supercritical steam plant by 5.3%-point

and 2.4%-point respectively

Kim et al. (2016): Compared thermodynamic performance of nine S-CO2 Brayton cycle layouts as bottoming cycles to a topping cycle of landfill gas fired gas turbine plant


◦ Concluded that recompression cycle not suitable for bottoming cycle application

Contributions of StudyContributions of StudyContributions of StudyContributions of Study

I thi t d Adapts S-CO2 cycles for efficient heat utilisation of

pulverised coal-fired furnace by using a topping and

In this study….

pulverised coal-fired furnace by using a topping and bottoming S-CO2 cycles, which were never explored before in the literature for coal-fired power plant

Investigates alternative S-CO2 cycle layouts as bottoming cycle to main S-CO2 cycleN f S CO l l f d l h New concept of S-CO2 cycle layout for residual heat energy utilisation

Integration of post-combustion CO capture with coal-fired Integration of post-combustion CO2 capture with coal-fired S-CO2 cycle power plant


Process Configurations and Process Configurations and DescriptionDescription

Simple recuperator closed Brayton cycleSimple recuperator closed Brayton cycle S-CO2 cycles take advantage of

increased density around critical region by operating thecritical region by operating the compressor inlet close to the critical point

The baseline closed BraytonThe baseline closed Brayton cycle is the simple regenerative closed Brayton cycle

Rapidly varying fluid propertiesRapidly varying fluid properties around the critical point leads to mismatch of heat capacity in the recuperator (pinch point problem)

Hence it is difficult to achieve high efficiency in simple s-CO2


Brayton cycle


Recompression S-CO2 cycle layoutRecompression S CO2 cycle layout

In the recompression cycle,

e

p ythe problem of heat capacity mismatch is resolved by splitting the flow into two

Tem

pera

ture streams

Of all the layouts, recompression layout gives p y gthe highest efficiency with a relatively simple configuration



Partial heating cycle layoutPartial heating cycle layout

Matching of the heat capacities achieved by splitting the flow at the compressor outletthe compressor outlet

A component count of different layouts showed that only the simple cycle and the partial heating cycle layout are simplerheating cycle layout are simpler than the recompression cycle layout

Hence, this cycle consider only h i l l hthe simple cycle, the

recompression cycle, partial heating and a new concept of S-CO2 cycle layout



New concept – Single recuperator recompression cycle layoutNew concept Single recuperator recompression cycle layout

Similar to the recompression layout except that the HTR y pwas eliminated leaving only one recuperator

Flow is split into two streams ow s sp t to two st ea sjust like the recompression cycle to balance the heat capacities between the precuperator hot stream and cold stream



Integration of single reheat recompression cycle with coal-fired furnace

APREC

T2 T4

T11

T12T14

T13

ECORHT

CHT CRHT

Hot fluegases

ARC MCLPHPG

HTR PCCLTRT3

T5 T10

T9

T17

ECOHT

RADRHT

HTR PCC Reboiler

LTR

T1T6 T8T7

T15T16

T18

RADHT

Hot fluegases B

Coal

Air Recompression S-CO2 cycle adopted due to its superior performance when compared to other layouts

The performance is further improved with a single stage of reheat Due to high level of recuperation, the flue gas leaves the furnace at

relatively high temperature (about 500 C)


relatively high temperature (about 500 C)


Utilisation of flue gas residual heat

A major drawback of coupling closed Brayton cycle to coal-fired furnace is the significant loss of heat through the hot flue gas leaving the furnace

If this exiting flue gas is not utilised it will represent the main cause of If this exiting flue gas is not utilised, it will represent the main cause of inefficiency in the power plant

Several options exist for utilising waste heat of flue gases from combustion processes:◦ Combined heat and power systems – some early operated coal-fired closed Brayton cycle were

used to generate electricity and produce heat for industrial heating (Oberhausen and Kashiraplant)p )

◦ Preheating part or all of the working fluid prior to main heat addition in the furnace

◦ Bottoming cycle – Echogen (USA) in the process of commercialising S-CO2 cycle as bottoming cycle utilising waste heat

◦ Preheating the incoming combustion air – common practice in conventional coal-fired plants

Adopted in this


pstudy


Overall plant configurations (Case A – Simple cycle bottoming)Overall plant configurations (Case A Simple cycle bottoming)



Overall plant configurations (Case B – Partial heating cycle p g ( g ybottoming)


Process Configurations and Process Configurations and

Overall plant configurations (Case C – New concept-Single DescriptionDescription

p g ( p grecuperator recompression cycle bottoming)


Steady StateSteady State MModelling in Aspen Plusodelling in Aspen PlusSteady State Steady State MModelling in Aspen Plusodelling in Aspen Plus

A model of the three cases of coal-fired S-CO2 cycle power plant with PCC was developed in Aspen Plus for comparison among the cases as well as with a benchmark coal-fired supercritical steam power plant

The plant systems/components modelled include coal mill, fans, preheaters, pulverised coal-fired furnace, ash removal components, flue gas desulfurization, s-CO2 cycles and PCC unit


furnace, ash removal components, flue gas desulfurization, s CO2 cycles and PCC unit

Steady StateSteady State MModelling in Aspen Plusodelling in Aspen PlusSteady State Steady State MModelling in Aspen Plusodelling in Aspen PlusSummary of assumptions and design point parametersSummary of assumptions and design point parametersParameter/variable ValueCoal feed (0C/bar/kg/s) 15/1.01/51.82Air (0C/bar) 15/1.01( )Excess air (%) 20Maximum cycle pressure (bar) 290HP & LP turbines inlet temperature (0C) 593Compressor inlet pressure (bar) 76Compressor inlet pressure (bar) 76Compressor inlet temperature (0C) 31Gas-CO2 TTD (0C) 30Preheater hot outlet temperature (0C) 116RecuperatorTTD (0C) 10Turbine isentropic efficiency (%) 93Main compressor isentropic efficiency (%) 90Recompression compressor isentropic efficiency (%) 89Recompression compressor isentropic efficiency (%) 89Fan isentropic efficiency (%) 80Generator efficiency (%) 98.4Ash distribution, fly/bottom ash (%) 80/20


Results and DiscussionsResults and DiscussionsResults and DiscussionsResults and DiscussionsStream tables

Stream

Case A P (bar) T (0C) m (kg/s)

Case B P (bar) T (0C) m (kg/s)

Case C P (bar) T (0C) m (kg/s)

Coal Air

1.01 15 51.82 1.01 15 540.88

1.01 15 51.82 1.01 15 540.88

1.01 15 51.82 1.01 15 540.88

Stream tables

Pry air Sec. air Pulv. Coal + airA

1.1 215 127.11 1.1 164.45 413.77 1.09 75.28 178.92 1.01 1010 592.7

1.1 215 127.11 1.1 152.40 413.77 1.09 75.28 178.92 1.01 1010 592.7

1.1 215 127.11 1.1 246.23 413.77 1.09 75.28 178.92 1.01 1010 592.7

B C D E F

1.01 495.25 592.7 1.01 252.54 592.7 1.01 116 592.7 0.98 116 587.68 1 05 123 94 587 68

1.01 495.25 592.7 1.01 244.55 592.7 1.01 116 592.7 0.98 116 587.68 1 05 123 94 587 68

1.01 495.25 592.7 1.01 306.70 592.7 1.01 116 592.7 0.98 116 587.68 1 05 123 94 587 68F

Flue to PCC T1 T2 T3

1.05 123.94 587.681.01 56.67 587.68 287.11 465.76 4028.23 282.82 593 4028.23 147.72 507.64 4028.23

1.05 123.94 587.681.01 56.67 587.68 287.11 465.76 4024.32 282.82 593 4024.32 147.72 507.64 4024.32

1.05 123.94 587.681.01 56.67 587.68 287.11 465.76 4148.37 282.82 593 4148.37 147.72 593 4148.37

T4 a1,b1,c1 a2,b2,c2 b8

145.51 593 4028.23 288.55 222.54 510.86 287.25 466.00 510.86

145.51 593 4024.32 288.70 305.80 528.51 287.25 466 528.51 290.00 69.79 152.86

145.51 593 4148.37 288.55 276.70 523.37 287.25 466.00 523.37


Results and DiscussionsResults and DiscussionsResults and DiscussionsResults and DiscussionsSummary of plants performanceSummary of plants performance

Parameters Case A No PCC

With PCC

Case B No PCC

With PCC

Case C No PCC

With PCC

HHV, MJ/kg 27.05 27.05 27.05 27.05 27.05 27.05 Input heat value, MJ 1401.87 1401.87 1401.87 1401.87 1401.87 1401.87Heat transferred to cycle (topping/bottoming), MW

1073.48/ 161.25

1073.00 /161.73

1068.50/167.12

1068.21 /167.40

1101.98/126.68

1101.95 /126.73(topp g/botto g), W

Furnace efficiency, % 88.08 88.08 88.14 88.14 87.64 87.64 Preheater duty, MW 87.59 87.61 82.06 82.15 122.50 122.38 Gross electric power (topping/bottoming), MWe

542.80/ 60.16

430.19/ 60.17

541.14/62.05

427.77/ 61.96

558.09/ 52.64

444.85/ 52.69(topp g/botto g), We

Cycle efficiency (topping/ bottoming), %

50.56/ 37.31

40.09/ 37.20

50.64/ 37.13

40.05/ 37.02

50.64/ 41.55

40.37/ 41.58

Overall cycle efficiency, % 48.83 39.71 48.82 39.63 49.71 40.49 Auxiliaries power, MW 10.49 19.49 10.49 19.49 10.49 19.49u a es powe , WNet electric power, MWe 592.48 470.87 592.71 470.25 600.24 478.05 Overall plant net efficiency, %

42.26 33.59 42.28 33.54 42.82 34.10


Results and DiscussionsResults and DiscussionsResults and DiscussionsResults and DiscussionsDistribution of the input heat valueDistribution of the input heat value

About half of the heat input transferred as radiant heat in the furnace

Total loss of heat is about 12% i.e. furnace efficiency about 88%

Hence, the addition of bottoming cycle bl ffi i ili i f f henables efficient utilisation of furnace heat

About 12% of the input heat value was recovered in the bottoming cycle heater


Results and DiscussionsResults and DiscussionsResults and DiscussionsResults and Discussions

Single reheat Efficiencies of the S-CO• At the same preheated air

level, partial heating has the hi h ffi iSingle reheat

supercritical steam turbine power plant, 24.1MPa/593 0C/593 0C

Efficiencies of the S-CO2cycle power plants are about 3% point higher than the benchmark steam power plant

highest efficiency• The new concept permits

higher air preheating level, and better performance at the high preheating level


ConclusionsConclusionsConclusionsConclusions A concept of coal-fired power plant using S-CO2 closed p p p g 2

Brayton cycles as power conversion systems and integrated with 90% post-combustion CO2 capture has been evaluated

The S-CO2 cycles were adapted for efficient utilization ofThe S CO2 cycles were adapted for efficient utilization of furnace heat by addition of bottoming cycle and air preheating

The thermodynamic performance evaluation highlights theThe thermodynamic performance evaluation highlights the promising potential of S-CO2 cycle for coal-fired power plant application (about 3% efficiency point higher than conventional steam power plant)p p )

Case C (the newly developed layout as bottoming cycle) allows the highest level of air preheating, thereby improving the plant net efficiencyt e p a t et e c e cy

There is need to consolidate these results by validating the performance of the coal-fired S-CO2 cycle power plant


ReferencesReferencesReferencesReferences Kim, M.S., Ahn, Y., Kim, B. and Lee, J.I. (2016), 'Study on the , , , , , , J ( ), y

supercritical CO2 power cycles for landfill gas firing gas turbine bottoming cycle', Energy, vol. 111, p. 893-909. DOI: http://dx.doi.org/10.1016/j.energy.2016.06.014

Le Moullec, Y. (2013), 'Conceptual study of a high efficiency coal-fired power plant with CO2 capture using a supercritical CO2 Brayton cycle', Energy, vol. 49, no. 0, p. 32-p y y gy p46. DOI: http://dx.doi.org/10.1016/j.energy.2012.10.022

Manente, G. and Lazzaretto, A. (2014), 'Innovative biomass to power conversion systems based on cascaded supercritical p y pCO2 Brayton cycles', Biomass and Bioenergy, vol. 69, no. 0, p. 155-168. DOI: http://dx.doi.org/10.1016/j.biombioe.2014.07.016.

Mecheri, M. and Le Moullec, Y. (2016), 'Supercritical CO2 Brayton cycles for coal-fired power plants', Energy, vol. 103, p. 758-771. DOI: http://dx.doi.org/10.1016/j.energy.2016.02.111


p g j gy

AcknowledgementsAcknowledgementsAcknowledgementsAcknowledgements

EU FP7 Marie Curie (R-D-CSPP-PSE PIRSES-GA 2013 612230)GA-2013-612230)

School of Energy & EnvironmentSoutheast University, ChinaSoutheast University, China

GE Power


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THERMODYNAMIC PERFORMANCE EVALUATION …...cycle) and bottoming (simple cycle) cycles for small to medium biomass plant as alternative to reciprocating IC or organic Rankine cycle