POWERGEN'S APPROACH TO THE IMPLEMENTATION OF F.G.D. J Evans and S K Reynolds .sx The paper outlines PowerGen's requirement for FGD plant and discusses the selection of station site for retro-fitting , the process type adopted and the main design requirements for the plant .sx The paper concentrates on the project , contract and commercial strategies for its implementation .sx Details are also given of PowerGen's first FGD plant at Ratcliffe-on-Soar power station near Nottingham .sx INTRODUCTION This paper discusses the sulphur abatement programme proposed by PowerGen and the necessity to install Flue Gas Desulphurisation ( FGD ) plants .sx The paper concentrates on PowerGen's technical & commercial approach to FGD and identifies the key features of the first plant proposed for Ratcliffe on Soar power station .sx SULPHUR ABATEMENT REQUIREMENTS .sx The effects of acid rain and the need for control on S02 emissions have been debated within the EEC for several years .sx These discussions culminated in the production of the 'Large Combustion Plant ( LCP ) Directive' , proposed in draft in December 1983 and agreed in principle in June 1988 .sx The Directive covers two distinct areas , namely :sx - .sx ( a ) New combustion plant The limits for S02 emissions etc are based on best available technology .sx ( b ) Existing combustion plant The limits are covered in terms of national emission limits , i.e a 'bubble' limit .sx These bubbles are set for each of the EEC member states and have three target implementation dates , 1993 , 1998 , and 2003 .sx Adoption of these bubble limits will necessitate reductions in S02 emission levels of 20% , 40% and 60% respectively for the UK ( based on the 1980 emissions) .sx THE REQUIREMENT FOR FGD RETROFITS .sx In order to meet its own sulphur abatement targets , PowerGen , as a power utility , now has a number of options available to it .sx These include the following :sx - .sx Increasing thermal efficiency of existing coal fired plant .sx Increased use of low sulphur fuel imports .sx Increased use of natural gas .sx Increased use of alternative energy supplies .sx Use of 'clean coal' technology .sx Retrofitting FGD plant to existing stations .sx PowerGen has examined the most economic and environmentally acceptable way of achieving the sulphur abatement targets .sx The process is however inextricably linked to almost all the major investment decisions currently facing the company .sx The commitment to reduce sulphur emissions is not just a question of assessing the amount of FGD required to reduce emissions from current emitters , it involves assessing both the current company emissions and the long term future emissions from any future plant .sx This is complicated by a number of factors :sx - .sx PowerGen has to compete for market share within the UK market which may change generation capacity within the company .sx Numerous gas turbine schemes are under consideration .sx Prediction of future coal sources ( and their sulphur levels ) is difficult .sx Taking the above into account , PowerGen applied to the Secretary of State for consent to retro-fit 4000MW of Flue Gas Desulphurisation Plant .sx SELECTION OF F.G.D. PROCESS TYPE .sx There are over 100 different types of FGD systems available worldwide , ranging from pilot plant processes to systems installed on several thousand megawatts of combustion plant .sx Detailed engineering studies on a number of different FGD process systems were carried out under the auspices of the C.E.G.B. and have been progressed further by PowerGen .sx Great emphasis has also been made on the operating experience of overseas FGD installations .sx In selecting the type of system to be used , PowerGen has taken into account the following points :sx - .sx The stations will operate on medium to high sulphur , high chloride coals .sx The main generation stations are large ( - 2000MW ) sites .sx The boiler units are large ( 500MW ) and are all 20-25 years old .sx The boiler units are required to operate for 38 months between major overhauls .sx The stations operate on a high load factor ( >80% ) .sx Production of a 'socially acceptable' by-product required .sx Minimisation of other effluents/waste products .sx Low lifetime cost required .sx Minimum maintenance requirement .sx Proven reference list of FGD process required .sx Considering the above factors , the Limestone/Gypsum process is considered the most suitable for PowerGen's retrofit FGD systems .sx This process is the most widely used FGD type worldwide and its selection is in line with world FGD trends .sx SELECTION OF STATION SITES FOR FGD RETROFITTING .sx In identifying which stations would be suitable for retro-fitting an FGD plant , a number of factors require consideration :sx - .sx ( a ) Commercial Aspects As FGD represents a major capital investment , maximum benefit ( in terms of the mass of sulphur removed ) must be gained from its installation .sx This entails considering only large stations , operating on high load factors ( i.e. base load operation ) and also firing high sulphur fuels .sx Coastal stations which may import low sulphur overseas coals are not considered at present .sx Remaining station life also needs to be taken into account in assessing the lifetime costs of the FGD system .sx ( b ) Environmental Aspects Given the size of the above stations ( 2000MW ) and the relatively high fuel sulphur content , an FGD system will require large quantities of reagent feedstock and will produce large quantities of by-products .sx Transport of feedstock and by-product at the power station is a major design consideration .sx The process will also produce large quantities of liquid effluent .sx ( c ) Station Factors Most of the large coal fired stations within PowerGen are now over 20 years old .sx Taking into account the above factors , the most suitable power stations identified within PowerGen were Ratcliffe-on-soar near Nottingham and Ferrybridge C near Leeds .sx Both are 2000MW base load stations .sx DESIGN REQUIREMENTS OF THE F.G.D. PLANT .sx Stack Emissions .sx The control of gaseous emissions are monitored and regulated in the UK by HM Inspectorate of Pollution ( HMIP) .sx They in turn report to the Department of the Environment ( DOE) .sx Regulations concerning the emissions from large combustion works ( >500MW thermal ) are covered in their 'Best Practicable Means Note No .sx 27'. This note however , only applies to new combustion plant sic !sx , there are no current regulations concerning the design of a retrofit FGD plant .sx In view of this , PowerGen proposed its own design parameters for the FGD plant which were discussed and agreed with HMIP and other relevant bodies .sx The principal parameters proposed were as follows :sx - .sx ( a ) Sulphur Dioxide Emissions The FGD plant will be designed to achieve 90% SO2 removal at the mean coal sulphur level with one absorber spray bank redundant .sx This redundant bank will serve as an operational spare and will also be brought into service if a high sulphur coal is fired .sx The plant is designed to handle coal sulphur levels up to 3% ( by wt ) and coal chloride levels up to 0.6% ( by wt) .sx ( b ) Stack Discharge Temperature The temperature of the emitted gases entering the chimney would be maintained at not less than 80 degC .sx This means that reheating of the flue gas is required .sx ( c ) Dust Emissions Dust emission from the process would not exceed 85 mg/m3 ( @15 degC , 1 bar , dry , 6%02) .sx Liquid Effluent Emissions .sx Due to the relatively high chloride content of UK coal , a liquid purge stream will be required to control the level of soluble chloride in the process .sx This stream will discharge calcium chloride into the local watercourse .sx The purge stream however contains not only calcium chloride but also flyash not removed in the ESPs , and contaminant trace metals from the coal , limestone and process water feeds .sx This stream requires treatment prior to discharge in the local water course to reduce these associated contaminants to acceptable levels .sx Treatment will be carried out in 2 x 100% water treatment plants and will result in a waste sludge being produced .sx This will require disposal , probably by landfill .sx The control of discharges into the rivers is controlled in the UK by the National Rivers Authority ( NRA) .sx The large size of PowerGen's stations , the high chloride content of UK coals and the relatively low flowrates of UK rivers result in FGD discharges being significant .sx Consequently the discharge limits applied by NRA are very tight .sx Discharges are normally applied in terms of maximum outfall concentrations , total mass discharges of selected species and total mass of chlorides discharged .sx Plant Availability .sx As a result of the Environmental Protection Act ( 1990 ) all large combustion plant sic !sx will be required to operate under an authorisation granted by HMIP .sx Whilst planned maintenance or occasional outages from a well designed and operated FGD plant may be acceptable , frequent outages from a poorly designed and operated plant will not .sx Thus there is requirement to design and operate the plant to high availability and reliability standards .sx Whilst HMIP have not stated an acceptable design availability , they are aware of values adopted by overseas utilities , in particular West Germany .sx In West Germany the legislation allows the combustion plant to be operated for a maximum of 10 days per year without the FGD operating ( there is a further proviso that each outage must not last longer than 72 hours) .sx This 10 day outage allowance means the FGD must be available for 355 days per year ( assuming continuous boiler operation ) - ie a plant availability of 97.5%. Thus this availability figure , in the absence of specific UK values , has been selected by PowerGen as a design figure .sx This represents a very high target value , particularly in relation to the PowerGen requirement for 38 months continual operation between overhauls and the boiler availability levels of approximately 90% currently being achieved .sx Quality of By Product .sx It is the stated aim of PowerGen to produce a socially beneficial by-product from its FGD systems , which with the Limestone/Gypsum process results in the production of a commercial grade gypsum .sx Local Planning Restrictions .sx Other restrictions on the process are imposed by local regulations such as visual aspects , noise levels ( construction and operating ) , road & rail traffic movements etc. These all have to be catered for in the plant design .sx All aspects associated with the design of the FGD plant are outlined in the PowerGen's Environmental Statement ( 2 ) which is produced for the Local Authorities , County Councils and other Regulatory Bodies , local groups , and the General Public .sx .sx PROJECT & CONTRACT STRATEGY .sx Type of Contract .sx Traditionally within the Electrical Supply Industry the project management of a large capital plant such as an FGD plant would have been achieved by the letting of several contracts .sx A main 'mechanical' contract would have covered the unit plant and most of the common plant , with separate contracts for the preliminary civils works , main civils works , mechanical handling equipment , electrical and C & I works .sx The contracts would also have been let against tight , comprehensive specifications produced in-house .sx Whilst this form of tendering procedure produces a clearly defined plant scope , it has a number of disadvantages :sx - .sx a large in-house team is required to produce the detailed specification and to monitor compliance of the tenders .sx the tenderers are forced into offering a plant design which may be slightly outside their experience and consequently carry a risk element .sx the tenderer has little room to optimise the plant design .sx conventional specifications tend to concentrate on component rather than system designs .sx there is little scope for fully evaluating all the plant options .sx there is a tendency to 'over-specify' the plant .sx numerous contracts would pose interface risks to PowerGen .sx In view of this , PowerGen decided to opt for a different contract strategy which would involve a central , lump sum , turn-key contract for each station , let against a performance type specification .sx The contract covers the main FGD plant , all the materials handling plant , the water treatment plant and all associated plant .sx It also encompassed mechanical , electrical , C & I , and all civil engineering and building works .sx PowerGen will only be placing separate contracts for the following minor contracts :sx - .sx Pre-application studies .sx Preliminary works design .sx Preliminary works .sx Unit transformers .sx Railway signalling .sx 11kv and 3.3kv switchgear mods .sx Landscaping .sx Finishing works .sx An important feature of the contract strategy is that the enquiry was issued simultaneously for both the Ratcliffe and Ferrybridge plants , with the contracts being linked together .sx This enables a high degree of standardisation to be achieved and the process designs of both plants will be identical .sx Selection of Tenderers .sx Considerable effort was made in the selection of suitable tenderers for the FGD project .sx Generally the tenderers consisted of a UK engineering company linked to an overseas group providing the process technology .sx