BIT's 3rd Annual International Symposium of Clean Coal Technology (CCT2014) September 1616-18, 2014
Venue : Taiyuan, China
Session 5 : Coal Gasification Technologies & Poly Generation
Partial Gasification of Pre-dried Pulverized Coal through Waste Heat Recovery – A Future Option CCT Chittatosh Bhattacharya, PhD Deputy Director(Technical ) & Associate Professor National Power Training Institute, Eastern Region – Durgapur, WB, India Date :17.9.2014
Time : 10.55 AM
To Meet Sustainable Power Demand Coal Power has A Proven Past A Progressive Present & A Promising Future With the support of low cost, low to high quality of coal resources to run at least for another Century (if not more) to provide affordable quality power for all with negotiable emission.
World Energy Outlook 2010
Starting with Electric Power Energy Realities Power Mix -World (2008), 20183 TWh Coal
Wind, 1%
Biomass, 1%
Solar, 0%
Hydro, 16%
Coal, 41%
OIL GAS Nuclear
Nuclear, 14%
Hydro Biomass GAS, 21%
OIL, 6%
The shift from coal power is not as fast as the growth of RE over the years !!
Introduction • “Big Five” Chinese Power Companies (Datang, Huaneng, Guodian, Huadian, and China Power Investment) & NTPC of India - The world’s biggest coal-fired power producers, & among the top developers of proposed new coal-fired plants. • Coal Pulverising - Energy intensive physical process performance is dependant on physio-chemical coal properties & responsible for complete burn out of coal. • Improving performance capability of pulveriser is limited by design & supply for a specific worst / best coal quality to be made available. 9/17/2014
• Any deterioration of coal quality may fail to meet the PC throughput demand for maximum steaming of boiler. • Improvement in pulveriser performance is linked to Low Rank coals(LRC) moisture drying capacity & associated heat rate penalty. • The existing coal moisture drying processes using regenerative APH in boilers are energy intensive, inefficient and inadequate for LRC particularly at higher Ambient Air Temperature (AAT) & Relative Humidity (RH). • Economics of LRC drying through waste heat recovery establishes significant reduction in fuel consumption, emission and improvement in overall boiler efficiency by way of reduction of heat lost for evaporative total coal moisture from the useful heat value of coal . 9/17/2014
Country wise Global Reserve : High Ash - Moisture LRC
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Burnard K; Bhattacharya, S. ; Power Gen. from Coal Ongoing Dev. Outlook, p 30; IEA 2011
Physical Constituents of Coal
Low Rank Coal (LRC) Coal Rank 9/17/2014
High Rank Coal as Volatile Matters
Problems associated with Low Rank Coals used in TPP Cost of Coal moisture may be equated to loss of coal heat value to provide drying energy resulting equivalent boiler Steaming Capacity loss, lowering Efficiency & adding more Emission Penalty. Common problems faced by PC fired TPS using low rank coals are: Deteriorating heating value of the coal, Inconsistent coal properties with adhered surface moisture, Presence of extraneous matters, High quantum of ash with high percentage of abrasive quartz. Extremely high electrical resistivity in ash due to Low sulfur %
A loss of 2% of coal heat content will make a variation of power pricing by USD 0.16 million (approx.)/year for 1000 MWe Plant. 9/17/2014
PC fired Boiler - Mill Performance Improvement Roadmap • To start with measurability of coal quality impact in mill. • Must attempt to delimit the impact of quality in performance. • Should incorporate process modification beyond existing and conventional options. • Should be economically viable & implementable alternatives to mitigate environmental obligations for coal. • Should be adoptable to existing declassified PC fired Boilers irrespective of sub critical or super critical regime of operation. • Should be adoptable as retrofit or in-process arrangement to coal fired Carbon Capture & Sequestration system as a sustainable Clean Coal Technology option. 9/17/2014
Coal Quality Impact Analysis in PC fired Utility & Partial Flue Gas Recirculation (PFGR) System through Pulveriser Experimental Investigations on fired coals of Thermal Power Plants Ultimate Analysis of an worst variety MCL coal & its effect in Heat Loss Carbon Hydrogen Oxygen Nitrogen Sulfur Ash
Water
HHV, MJ/kg
LHV, MJ/kg
10.88
10.11
%wt (ar)
28.921
1.833
5.431
0.543
0.272
%wt (mf)
34.025
2.157
6.39
0.639
0.319
56.47
0
12.8
12.32
%wt (amf)
78.165
4.954
14.68
1.46
0.734
0
0
29.4
28.31
2.847
SO2 – 0.005
0.315
Wet Stack gas – 4.227
wt CO2 – Evaporated O2 - 0 stack Moisture 1.06 Kg / Kg coal
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48 15
Dry Stack gas – 3.912
Coal quality impact analysis in PC power generation process & PFGR Change Of Useful Heat Value With Varied COAL Moisture of MCL Coal
Heat (%) lost in Drying WCL Coal
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Coal Heat (%) lost in Drying MCL Coal
Coal Heat (%) lost to Dry Up ECL Coal
Coal quality impact analysis in PC power generation process & PFGR
Chimney
BOILER FFS
PFGR ESP
ID Fan
MDC
FD Fan
The collected flue gas at 460-530 0C (60 - 100% MCR) will improve average mill inlet PA Temp. to 315430 0C .
GR Fan
Mill PA Fan
Partial Flue Gas Recirculation through Pulveriser (Scheme) 9/17/2014
Coal quality impact analysis in PC power generation process & PFGR
Field Study Findings
Study conducted for 210 MWe unit operating at 155 kg/cm2 & 535 0C. The design coal feeding at 100% MCR = 109 TPH @ 7% -Max. Total Moisture, GCV -19.888MJ/Kg & 50 HGI. Change in ROM coal (AR) throughput @ 46 HGI, 15% TM & GCV 15.157 MJ/kg - 146 TPH. The Max. hot PA Temp. :3340C (APH O/L).Maximum drying capacity/pulverizer- 12 TPH (TM of coal) (presuming 1% residual moisture in PC leaving mill). Change in coal throughput demand with experimental coal @ GCV 10.88MJ/Kg & 15% TM, 50 HGI - 200 TPH (for 100% MCR without FO firing) presuming 88.5% ηboiler The 100 TPH / mill coal flow - achievable by enhancing drying capacity matching excess TM with PFGR through PA Fan intake tapping FG from Eco. I/L at a temperature of 526 0C & at a rate 112 TPH for a total PA flow of 119 TPH / mill ≈ 14 % of total FG entering APH.
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Coal quality impact analysis in PC power generation process & PFGR
Result Optimum Pulverizing Capacity : Maximum experimental PC output/mill - 100 TPH (with PFGR) Maximum experimental PC output/mill – 83.75 TPH (W/out PFGR) Without PFGR steaming capacity - 197 MWe @ 88 88..5% ƞboiler With PFGR steaming capacity - 210 MWe @ 88 88..5% ƞboiler. Minimizing NOx The additional NOx reduction with PFGR ≈ 0.07 kg/GJ approx. with SOFA arrangement resulting 70-73% of total NOx (total equivalent NO2 - 0.6896 kg/GJ) reduction amounting total equivalent NO2 emission through stack reduced to 0.1888 kg/GJ. ( on the basis of evaluation through IECM© software) 9/17/2014
Integrated Drying and Partial Gasification for Low Rank Coal-Power options
Typical impact on flame front velocity due to VM reduction of coal Partial VM loss is unavoidable due to hot air drying or steam drying without proper arrangement to capture the escaped VM in the drying process prior coal feeding to pulverizer.
↑
→
The Heat Value lost to dry up the coal is significant if the drying process is lined up to consume useful fuel heat value in the thermal power generation process.
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Typical weight loss, drying up and partial devolatilisation for sub bituminous PC with constant rate of heating.
Integrated Drying and partial gasification for low grade coal-power options
Typical Improvement in Flame Front Velocity of PC with coal beneficiation at constant coal VM & devolatilisation rate.
Flame Front Velocity m/s
Ash - 5 % by wt
Fuel Rich – devolatilisation zone With Partial FGR through mill
Excess Air – controlled combustion zone with oxidizing secondary air
The CO2 enrichment in dry stack gas suggests a fuel rich coal drying with PFGR & increasing Flue gas - Air / PC Ratio opportunity to partially dry the CO % in dry stack gas at various excess air 2 coal through waste heat recovery % for MCL coal. from FG at ID fan discharge upstream of stack resulting more opportunity for coal heat value saving to generate steam than to dry the coal along partial PC gasification at mill exit with PFGR 9/17/2014
Ash - 40 % by wt
Integrated Drying and partial gasification for low grade coal-power options
PFGR© requirement /kg MCL coal at various moisture % & available FG temperature (0C)
FG waste heat recovery drying in a fluidized bed in ID Fan O/L duct improves mill drying capacity and provide opportunity for partial coal gasification of PC with recirculated FG 9/17/2014
Moisture Removal – 40% Moisture Removal – 30% Moisture Removal – 15% Moisture Removal – 10% Moisture Removal – 6.5%
Integrated Drying and partial gasification for low grade coal-power options
Further improvement - Integrated drying & partial coal gasification system with PFGR©
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Performance Impact of Air Preheater on Overall Equipment Efficiency Boiler Input Devices
FD & PA Fans Pulverizers Burners Economizer
Boiler Output Devices Environmental Emission Control Devices
Boiler Operation Electrostatic Precipitators Combustion Control Bag houses SCR FGD ID Fans WB/ Mill
1
Evaluation of APH Leakage 4
1
Hot Flue Gas
2
Hot Air
2
3 ID Fan P
FD FAN + P
PA FAN
APH Bypassing APH Gas Side
3
Ambient Cold Air
APH Gas Side
4
Ambient Cold Air
APH Bypassing
APH helps to dry up pulverized coal with hot primary air, rapid attaining of ignition temperature and creating turbulence with more volumetric flow of Secondary air. 9/17/2014
Effect of AAT in Performance Ambient air temperature (AAT) affects - mass flow rate (ma), coefficient of heat capacity (Cpa); density, humidity ratio (moisture content capacity of air on RH)
Boiler (Air/Flue gas) ・ Quantity of Air flow（ma, ）、 when (Tae) AAT Hot Air
・ (Tae) AAT
Humidity Ratio
・ Humidity Ratio ・ (Tae) AAT
・ As (Tae) AAT
ma
Flue Gas
DPh
mg Tge
Heat loss to dry air
ηAPH ΔPh（Δp Δpa :O/L – ΔPg I/L）
thus Air leakage
ΔPa
Tae
ΔPg
m L
FD/PA Fan
The result of Plant Findings speaks for it…..
Tgl
ESP 9/17/2014
Coal moisture removal economics with waste heat recovery
Result - Coal Moisture Economics ( For 210 MWe TPP) Reference Coal MCL Coal WCL Coal Non-coking Gr. F Non-coking Gr. D Coal Rank “As Recd” HHV (MJ/Kg) 10.878 19.526 Coal Price Unit Rs. (’07) Rs. (’07) Coal Price / MT 440.00 1210.00 As Received Coal 15.00 19.50 Moisture (wt %) Ref. Case : 2% decrease in “As Fired” coal moisture As fired coal Moist. (wt %) 13.00 17.50 “As fired” LHV with 2% less moisture[wt%(ar)] in 10.404 18.889 coal (MJ/Kg)
Waste heat recovery savings in equivalent “As Received” coal quantity in MTPD 9/17/2014
139.45
85.79
ECL Coal Non-coking Gr. D
20.398 RS. (’07) 1360.00 1.95 0.0 20.111
212.38
CONCLUSION Improvement in “as received” to “as fired” coal quality with more UHV of PC is achievable with IDPCG, waste heat recovery based coal drying, resulting least wet FG loss through stack. Reduced specific coal consumption / kg steam with minimization of loss of coal heat value to dry up wet coal. Retrofitting feasibility with near pure oxy – coal combustion technology for enriched CO2 capture opportunity for economic & viable emission management through sequestration as a CCT project. 9/17/2014
References Bhattacharya, C.; Sarkar, H. S.; “Economic Assessment of Utilization of Beneficiated Indian Power Coal for Thermal Power Generation” (April 2003); National Symposium (SRP-2003) CMERI (CSIR)/Durgapur/INDIA .(Abstracted PP: 46-47). Bhattacharya, C.; Mitra A.K.; "Improving Pulverizer Output by Partial Flue gas Recirculation” Proceedings of International Conference on “Advances in Energy Research”;pp 485-491 (ICAER) 12-14 Dec, 2007, IIT Mumbai, India; Macmillan India Ltd(ISBN 10:0230-63432-X). Bhattacharya, C.; Banerjee, N; 2011; “Integrated drying and partial coal gasification for low NOx Pulverized coal fired boiler”, Proc. of ASME 2011 Power-ICOPE Conference, Vol. I , pp. 293-300 (ISBN: 978-0-7918-4459-5). http://dx.doi.org./10.1115/POWER2011-55108 Bhattacharya, C.; Banerjee, N.; Sarkar, H.S.; “Economics of Removal of Coal Moisture in Thermal Power Generation with Waste Heat Recovery, “International Journal Of Emerging Technology and Advanced Engineering, Vol. 3, Special Issue 3:ICERTSD 2013 February 2013, pp 22-28.[ISSN 2250 2459] http://www.ijetae.com/files/Conference%20ICERTSD-2013/IJETAE_ICERTSD_0213_04.pdf Bhattacharya, C.; Sengupta, B., “Effect of Ambient Air Temperature on the Performance of Regenerative Air Preheater of Pulverised Coal Fired Boilers” Proc. of 4th Int. Conf. on Advances in Energy Res.; ICAER 2013, pp 63-69; IIT Bombay, 10-12 Dec.’13; ISBN :978-81-928795-0-5.
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