Fluidized Bed Technologies for High Ash Indian Coals –

A Techno-Economic Evaluation

Dr. D.N. Reddy, Director Dr. V.K. Sethi, Research Adviser

Centre for Energy Technology, University College of Engineering (Autonomous)

Osmania University, Hyderabad – 500 007, India.

INDIAN POWER SECTOR - TOWARDS SUSTAINABLE POWER DEVELOPMENT

Total Installed Capacity … 103,000 MW Thermal Generation … over 70 % Although no GHG reduction targets for India but it has taken

steps through adoption of Combined cycles, Co-generation, Coal beneficiation,Plant Performance optimization

Long term measures like adoption of Clean coal technologies; IGCC, FBC, Supercritical technologies

Clean Development Mechanism (CDM) conceived to reduce cost of GHG mitigation, while promoting sustainable development as per Framework Convention on Climate change (FCCC) is being implemented

SIGNIFICANCE OF THE PRESENT STUDY...

Environmentally benign Clean Coal Technology of advanced Fluidized Bed Combustion is an ideal technology for high ash coals

Statutory use of washed coal for TPS >1000 km from the pit head calls for setting up of washeries > 85 Million tons / annum.

Use of Washery rejects & Middling for Power generation calls for adoption of CFBC technology

The present paper deals with the techno-economic and transfer of technology aspects of Clean coal technology in general and CFBC in particular for inferior coals & in refurbishment of old polluting plants

Energy Efficient Technologies

Technologies on Anvil for Power generation using high ash Indian coals:Supercritical (SCR) & Ultra – supercritical (USC)Integrated Gasification Combined Cycle (IGCC)Fluidized Bed Combustion

VISION 2020

PROGRAM

Post combustion Clean-up-Desulfurization

(FGC systems) Supercritical

In-combustion Clean-up Fluidized bed

combustion (CFBC, PFBC, AFBC)

Gasification using + fluidized bed, moving bed or Entrant bed Gasifiers

Pre combustion Clean-up beneficiation/washing

Technologies for utilization of Coal for Power Generation with minimal pollutants discharged to the atmosphere (Reduced CO2, Sox, Nox, SPM) at high conversion efficiency……….W.C.I.

CLEAN COAL TECHNOLOGIES

Fig.5 EFFICIENCY IMPROVEMENT FORECASTCONVENTIONAL Vs IGCC(Courtesy BHEL)

60

55

50

45

40

35

301990 1995 2000 2005 2010

Year of commercial use

Net

The

rma

l Effi

cie

ncy

(%)

Ceramic gasturbine

566 Co 600 Co623 Co

1300 Co 1500 Co

540 Co

650 Co1184 Co

IGCC (15 C Amb)

IGCC (Indian Condition)

Super Critical PC Power Plant (15 C Amb.)o

Super Critical PC Power Plant (Indian Condition)o

Sub Critical PC Power Plant (Indian Condition)

The Principal advantages of supercritical steam cycles are :-

Reduced fuel costs due to improved thermal efficiencyCO2 emissions reduced by about 15%, per unit of electricity generated, when compared with typical existing sub-critical plantWell proven technology with excellent availability, comparable with that of existing sub-critical plantVery good part-load efficiencies, typically half the drop in efficiency experienced by sub-critical plantPlant costs comparable with sub-critical technology and less than other clean coal technologies.Very low emissions of nitorgen oxides (Nox) sulfur oxide (Sox) and particulate achievable using modern flue gas clean-up equipment etc.

Front line issues are to be reolved

Development of high temperature creep resistant alloy steelsTurbine material development

Super Critical Technology- Indian Perspective

Mega power policy of setting up of coal fired supercritical/Ultra Supercritical units at pit-headCost of generation is least for pithead washed coal-fired unit amongst all other supercritical units.The optimum parameter for Indian conditions is suggested as 246 kg/cm2 & 538/566C.Based on transfer of technology model as per logic diagram (shown next) the velocity of transfer of technology for supercritical units is 2 ½ from the year 2000.

IGCC TECHNOLOGY ... Gasification of coal is the cleanest way of utilization of

coal, while combined cycle power generation gives the highest efficiency.

Integration of these two technologies in IGCC power generation offers the benefits of very low emissions and efficiencies of the order of 44-48%.

The comparative indices show that in case of IGCC, emission of particulate, NOx and SOx are:

7.1%, 20% and 16%, respectively, of the corresponding emissions from PC plant.

Environmental performance of IGCC thus far exceeds that of conventional and even supercritical plants.

Three major areas of technology that will contribute to improvements in IGCC are :

hot gas de-sulfurisation hot gas particulate removal advanced turbine systems

Commercialization of IGCC needs technology demonstration at an intermediate scale of about 100 MW to address the issues such as:

hot gas clean ups and system optimization and to

establish reliability and performance.

This would also enable to design an optimum module for air blown gasification, which in multiples would constitute a commercial size plant in the range of 300-600 MW.

Technology transfer related issues and techno-economic analysis vis-à-vis CFBC are covered in the paper

Identified R&D Areas in IGCC are:

Process optimization of selected gasification process

Improvement of design and reliability of plant components & Resource Optimization

Optimization of overall plant heat integration and layout

Hot gas cleanup

COAL GASIFICATION – SELECTION OF GASIFICATION PROCESS

The fluidised bed process has many technical and environmental advantages over the moving bed process, such as,

The fluidised bed can use any amount of fines whereas in the moving bed only 10% of fines can be used.

In the fluidized bed process, hydrocarbon, liquid by-products such as tar, oil and gas-liquor are not produced and, hence, the pollution is reduced.

High ash coals can also be successfully gasified in the fluidised bed.

Experience on the fluidized bed process is, very limited in the country.

Internationally, the experience gained so far is only for low ash coals.

Thus there is a need for taking up extensive R&D on IGCC Pilot Plant using high ash (40-50% Ash) Indian Coal

Technology-related issues in IGCC

Design of Advanced gasifiers (optimum gas

composition, optimum scale-up etc.)

Hot gas cleaning (de-sulphurisation and particulate

removal)

Advanced gas turbines (blade design to sustain ash

laden gas)

CO2 emission abatement in IGCC Power Plants

Operating conditions of IGCC plants in transient stage

Configuration of an optimized system for IGCC

Fuel – related issues

In a Raw Pet-Coke and refinery residue based IGCC Plant System optimization, particularly the balance of plant Optimized Heat balance diagrams Scaling up of gasifiers to optimum size

In a Coal/Lignite based IGCC Plant Process & Plant conceptual design De-sulfurization of syngas of high sulfur coal and lignite Optimized Heat balance diagrams Super critical Vs IGCC in Indian context Application of ASME PTC-47 code for IGCC for high ash coals

and lignite

SOME IMPORTANT FINDINGS ON TECHNOLOGY ASPECTS OF IGCC...

Reactive solid sorbent de-sulfurization combined with hot gas cleaning through ash and sorbent particle removal provides for higher energy efficiency to the extend of 4-7%.

The current Capital cost of building an IGCC power plant is of the order of Rupees 6 Crore/ MW.

Improvements in hot gas cleaning coupled with Cycle optimization shall bring down the cost drastically to a level of $ 1000/kW or about Rupees 4.5 crore/MW

The efficiency of refinery bottom based IGCC unit will be about 2% higher than that of coal based IGCC unit.

Refinery based IGCC plants - Advantages Co-generation of steam Co-production of hydrogen gas & recovery of sulfur

element No use of limestone, as required for CFBC technology No requirement of extra land for disposal of solid waste

In the long run the refinery based IGCC technology is equally attractive to coal based IGCC from economic and environmental considerations.

A GENERALIZED SCHEME FOR TRANSFER OF TECHNOLOGY

The first step in the scheme is to disintegrate the Power plant concept into components, sub systems, production chain, production technologies

Next step is the Value addition to each element of the production chain

Assessment of necessity of Import and Calculation of indigenous production share

Calculation of Velocity of the Transfer of Technology both at normal pace as well as accelerated pace

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Typical results of the velocity of TOT are : - (With year 2000 as base)

IGCC (oxygen blown) - Pet coke Normal pace ---- 5 yearsAccelerated ---- 2 years

IGCC (Air Blown) ---- CoalNormal pace ---- 7 yearsAccelerated ---- 5 years

)

SOME FINDINGS RELATED TO TRANSFER OF TECHNOLGOY (TOT)

At present it may be prudent to implement the project in phased manner to absorb the risk of gasifier in the total project wrap-up guarantees

A Technology Transfer model for determination of velocity of Transfer of Technology (TOT) is an useful tool for TOT of a frontier technology from a developed economy to a developing economy

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PHASED CONSTRUCTION

Circulating fluidized Bed CombustionCirculating Fluidized Bed Combustion (CFBC) technology has selectively been applied in India for firing high sulphur refinery residues, lignite, etc. In the overall terms the CFBC is superior to PC as follows:

- Lower NOx formation and the ability to capture SO2

with limestone injection the furnace. - Good combustion efficiencies comparable to PC -The heat transfer coefficient of the CFB furnace is nearly double that of PC which makes the furnace compact.-   Fuel Flexibility: The CFB can handle a wide range of fuels such as inferior coal, washery rejects, lignite, anthracite, petroleum coke and agricultural waste

      CFBC Vs Other Clean Coal Technologies

At present pulverized fuel firing with FGD are less costly than prevailing IGCC technology. However, firing in CFB Boiler is still more economical when using high sulfur lignite and low-grade coals and rejects.

ITEM CFBC PF+FGD/SCR IGCC

Cycle Eff. % 34.8 36.7 41-42

Relative Capital Cost/kW

1.0 1.03-1.19 1.15-1.42

Relative O&M Cost/kW

1.0 1.49 0.8-0.98

Revamping of Old Polluting PC Boilers by CFBC Boilers

Renovation & Modernization (R&M) and Life Extension (LE) of old power plants is a cost-effective option as compared to adding up green field plant capacities.

Growing environmental regulations would force many utilities within the country to go for revamping of these polluting old power plants using environmentally benign technology.

A mere refurbishment by the same type of new boiler would not provide the right solution today. There is desperate need to revamp aging power boilers in India with environmentally friendly technology, which will improve the thermal as well as environmental performance.

CFBC offers a promising technology on this front. This calls for boiler sizing within the constraints of an old polluting plant

Some representative results follow ...