Clean power from Estonia's oil shale

Eesti and Balti, owned and operated by Narva Power, are the largest oil shale fired power plants in the world, with a combined gross installed design capacity of 2 900 MWe and 582 MWt. They are the two principal electricity generating plants of Estonia, accounting for more than 95 per cent of the country's net electricity production. The primary business of Narva Power, headquartered in the town of Narva, about 210 km east of Tallinn, close to the Russian border, is electricity generation. But heat is also produced and sold to residential and industrial customers in the Narva region.

The oil shale fired at Eesti and Balti comes from mines owned and operated by Eesti Põlevkivi in the Narva region.

The Eesti and Balti plants

Eesti. Eesti, with an installed gross design capacity of 1610 MWe and 74 MWt, is the world's largest thermal power plant burning low-grade oil shale. It is located about 25 km south west of Narva.

Eesti has eight independent 200 MWe blocks. Each block comprises two pulverised fuel boilers, supplied by Taganrog of Russia, and one steam turbine shared between each pair of boilers. The eight turbines were manufactured by LMZ of St Petersburg and are of type K-200-130. They are condensing turbines with reheating capabilities. Seven have a nominal output of 200 MWe, while one has a nominal output of 210 MWe.

The eight blocks of the Eesti power plant were commissioned between 1969 and 1973.

Seven blocks, with fourteen of the plant's sixteen boilers, are currently in operation, while block 8 has been taken out of service for repowering.

Boiler units 8A and 8B have been dismantled and are to be replaced by two new circulating fluidised bed (CFB) boilers as part of the repowering project.

Balti. The Balti power plant was built between 1959 and 1966 and is located 5 km to the south-west of Narva. The plant property comprises 1 707 hectares of land. The plant originally had fourteen generators with a total generating capacity of 1 624 MWe and 505 MWt, but its continuous rated electrical capacity has now been reduced to 1290 MWe due to derating as well as decommissioning of some older blocks.

In addition to electrical power generation, Balti provides Narva with hot water for heating and some steam for industrial users.

The Balti plant has generated in the region of 260 TWh of electrical energy during its 40 years of operation.

The older part of the power plant comprises four (originally eight) 100 MWe condensing turbines, two of which have controlled extraction for the delivery of district heat. Steam is supplied to the turbines from eighteen pulverised fuel fired boilers, each with a capacity of 53 kg/s (190 t/h), feeding a common header.

The newer part of the plant comprises four 200 MWe steam turbines with reheat, in block form, with two pulverised fuel fired boilers with a capacity of 78 kg/s (280 t/h) per turbine.

Power from the 100 MWe blocks is delivered to a 110 kV and a 220 kV system, while the 200 MWe blocks serve a 330 kV system.

In the Balti project, unit 11 (one of the 200 MWe blocks) will be repowered. As with Eesti, the two pulverised fuel boilers will be replaced with CFBs and the existing steam turbine upgraded.

Investing in the future

The Narva Power investment programme has been developed to secure long-term electricity and heat production in Estonia based on local oil shale, with minimum environmental impact and maximum efficiency.

The investment programme comprises three distinct elements:

• Repowering projects.

• Renovation projects. And

• Environmental remediation.

The three main objectives of the investment programme are:

• To reduce the total level of SO2 emissions to enable Estonia to meet its international environmental obligations.

• To address other environmental issues at the power plants such as particulate emissions, ash pond rehabilitation, soil and ground water contamination and water treatment plant renovation. And

• To improve the efficiency and reliability of the power plants.

The repowering projects, representing almost 70 per cent of the total cost of the total Narva Power investment programme, are being undertaken on the basis of a turnkey EPC contract with Foster Wheeler. Fortum Engineering is acting as owner's engineer, providing design review, on-site inspection and monitoring, on-site engineering management, shop inspection, support for performance testing and various other expert services.

Narva Power issued a limited notice to proceed to Foster Wheeler on 28 May 2001 in respect of the repowering projects in order to allow initial foundation design, engineering work and the purchase of materials and manufacture of pressure parts to proceed. On this basis, the expected timetable for undertaking and completing the repowering projects is as follows:

Oil shale is a difficult fuel, with low calorific value (averaging 8.2 MJ/kg in Estonia) and a high level of corrosion-promoting ash content. Feasibility studies and laboratory testing, including combustion tests on Estonian oil shale, conducted in co-operation with leading boiler manufacturers over the past seven years, have indicated the suitability of using CFB technology to burn this fuel efficiently and cleanly. In addition, Tallinn Technical University undertook a generic environmental impact assessment for an oil shale fired CFB.

The main advantages of using CFBs to burn oil shale, compared with pulverised fuel technology, are:

• Significant reduction of emissions to the atmosphere: SO2 is reduced by about 95 per cent; NOx by around 55 per cent; CO2 by some 23 per cent; particulates by approximately 97 per cent. These benefits are achieved without the need for separate desulphurisation or limestone feeding, as the limestone present in the oil shale coupled with the boiler design features is sufficient.

• An increase in the gross MCR output of the units from 170 MWe and 180 MWe, at Balti and Eesti respectively, to 215 MWe following repowering.

• An increase in the efficiency of each unit from 30 per cent to 36.5 per cent, which is expected to lead to a saving in fuel costs of over 20 per cent and a reduction in emissions per unit of electricity or heat produced. And

• A significant reduction in operation and maintenance costs.

The repowering of Eesti block 8 and Balti block 11 is scheduled to be completed by the end of 2004, allowing Narva Power to achieve an annual net generation of up to 6600 GWh per annum. Furthermore, this will be achieved within the annual maximum limit of 38 000 t of SO2 emissions imposed by the Finnish-Estonian treaty, which becomes effective in 2005.

The repowering process for each block is similar, involving, as well as the replacement of the existing pulverised oil shale boilers with new CFB boilers, other balance-of-plant renovations.

At Balti, a new heat source for the existing heating system will be provided to replace the heat supply from the existing older plant. Additionally, a number of oil-burning package boilers will be installed to provide peaking and backup heat once the cogeneration units are taken out of service after the commissioning of Block 11.

The existing boilers and auxiliaries at both blocks, including all ducts up to the stacks, will be dismantled prior to the repowering with only the boiler building walls remaining.

The repowering of Eesti block 8 will include the erection of the two CFB boilers with auxiliaries, overhauling of the steam turbine (including replacement of the low pressure rotor), rebuilding of the ESP, upgrading of instrumentation and control and electrical systems and upgrading of ash handling capabilities.

Scope of work

The scope of work in the EPC repowering contract will include the following items of major equipment and plant facilities:

Boilers

Demolition of the existing pulverised fuel boilers and replacement with natural circulating, drum-type CFBs which will operate using a wide range of fuels, including a lower heating calorific value range of 8.0 MJ/kg to 11.0 MJ/kg.

The CFBs are single reheat with INTREX superheaters, and have additional features for optimum combustion of oil shale. Steam will be generated at 540 °C and 131/27 bar (g).

Each repowered block will use two 300 MWt boilers to supply a single steam turbine. The boilers will be designed for 8000 hours of operation per year and a total design life of 240 000 hours of operation, with 2000 cold starts.

The boilers are designed to operate with a daily load swing of between 40 per cent and 100 per cent of the MCR output.

CFB technology has several advantages when it comes to burning lower grade solid fuels. Combustion takes place in the lower furnace in a bed fluidised by an upflow of combustion air. With combustion concentrated in the lower furnace, the CFB is capable of higher heat transfer and hence higher efficiency. The circulating fluidised bed boiler is also better suited for capture of SO2 due to the constant mixing action of the bed, as well as reduced NOx production by allowing better control of combustion air.

The scope of work for the boiler at Balti block 11 will be the same as for Eesti block 8 but with the inclusion of district heating equipment.

Steam turbine generators

The existing LMZ Type K-200-130-6 turbine in Eesti block 8 was commissioned in 1973. The Balti block 11 turbine, LMZ Type K-200-2AT3, was commissioned in 1965.

For both units the scope of work will include replacement of the low pressure rotors and stationary blading as well as associated modifications.

The high pressure and intermediate pressure sections of both turbines will be overhauled and the turbine controls for both units will be upgraded.

The installed generators were manufactured by Electrosila of St Petersburg. There is a model TBB-200-24 at Eesti block 8 and a model TBF-200-2AT3 at Balti block 11. Both of the generators will be upgraded to provide a continuous rating of 215 MWe at a 0.85 power factor.

Particulate control

One ESP will be provided for each boiler. The ESPs will be designed to operate under all operating conditions from initial plant start-up to complete shutdown of the plant and will achieve a particulate emissions limit of 30 mg/Nm3.

Ash handling system

The ash handling system will be fully co-ordinated with the steam generator design requirements, ESPs and bulk material handling equipment and will be the same as the existing hydraulic ash and pneumatic disposal systems.

Generator and transformer protection

The existing protection systems for the generator step-up transformers and unit auxiliary transformers will be refurbished.

Notice to proceed

With the issuing of the official notice to proceed on 1 April, work on repowering Balti block 11 is now underway.

Meanwhile, work is well advanced and on schedule for the Eesti block 8 repowering project. Civil works started in mid-October last year and steel structural work began at the beginning of March this year. Boiler erection will begin this August, with mechanical completion due in August 2003.
Tables

Gross installed design capacities of the Eesti and Balti plants