Bulgaria is replacing two nuclear plants with a 670 MW lignite fired power station in the country’s first IPP project. How will the new baseload facility meet its promise of limited environmental impact and be complete in only 36 months?

Jerome Bridon, Alstom, France

Bulgaria joined the European Union (EU) In January 2007 under strict conditions – these included the promise that it would overhaul its power sector, partly by closing the two old Soviet-style Kozluduy nuclear power plants. To meet the shortfall of electricity that this decommissioning would create, a plan got under way to build a plant to run on domestic lignite, but to have limited environmental impact. Bulgaria would have a new power station at the site of the Maritza East plant and would invite the private sector to build it. In 2005, US independent power producer (IPP) AES won the contract to build the 670 MW plant, to be called AES 3-C Maritza East 1. As full turnkey EPC contractor for the project, Alstom now has the task of delivering the power station that will run 24/7 and meet emissions criteria of the Bulgarian government, the EU and other relevant authorities. As the project that is receiving the largest foreign direct investment in the history of Bulgaria, its success may pave the way for future IPP projects.

Reviving a dormant project

Originally, Alstom and AES were to undertake the project under a contract signed in April 2002. But the scheme became dormant because of the difficulty of arranging finance for it. This issue was solved in 2005 when France’s government stepped in with further financing through COFACE. This group of 22 banks, led by French bank Calyon — the financing and investment banking business created by the merger of Crédit Agricole and Crédit Lyonnais — provided some 70 per cent of the financing. The remainder would come from the French and German export credit agencies and equity from AES.

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With all the necessary financing in place, pre-engineering began in December 2005. The first shovelling that marked the official beginning of the project took place in June 2006, and the contract giving the full notice to proceed was signed in August 2006.

Under its turnkey deal, Alstom is providing complete power station engineering; two turbine generator sets and boilers; the water–steam cycle; the balance of plant; construction services; lignite and ash handling systems; and electrical and instrumentation and control systems, which include a distributed control system based on Alstom’s Alspa brand.

Plant design

The project is near the town of Galabovo. This is 40 km south-east of Stara Zagora and 250 km south-east of the capital, Sofia.

In addition to helping Bulgaria meet its overall national objectives for additional power generation, the new plant will also help the government meet the lignite extraction targets for the Maritza East mines. The use of indigenous lignite will also have a beneficial effect on the country’s foreign trade balance because its price is about 25 to 50 per cent lower than that of liquid fuels and natural gas, which are obtained primarily through imports.

Lignite will arrive by train at the dedicated delivery stations at the power plant. Conveyors will then take it either to a storage area or directly to the boiler bunkers. A coarse crusher and then a fine crusher will pulverize the fuel before its injection into the boiler. Limestone for desulphurization will also arrive by train and will be stockpiled before a conveyor takes it to its treatment area.

Two tower-type boilers, each 110 m high each with a large furnace volume will burn the fuel, which has a low calorific value. Each boiler has six mills and six low-NOx burners at heights of 12 to 25 m.

At full output, the two identical steam generator units will produce a combined output of 670 MW. Planned maintenance activities and estimated forced outages will result in an effective annual capacity factor of 95 per cent. In other words, the plant is expected to operate for about 8300 hours a year. Such high availability can be achieved only with state-of-the-art design and careful selection of key components, especially in the case of the flue gas back-end.

In each block, steam from the boiler will enter a 350 MW three-casing steam turbine, each of which has an HP, IP and LP section. HP steam is delivered from the boiler at 540 °C and 16 670 kPa, IP steam at 540 °C and 3900 kPa.

In a first for Alstom, the steam turbines have a lateral exhaust that allows the height of the turbine hall to remain low. With the condenser at the side of the turbine rather than underneath it, the use of concrete and construction materials is kept low, saving material costs and, ultimately, capital costs.

Clean power

The project company is committed to minimizing the environmental impact of the construction and the operation. AES 3-C Maritza East 1 will use state-of-the-art technology and have pollution control equipment that meets World Bank, EU and Bulgarian air and water pollution control standards. Its efficiency will be greater, and its emissions of sulphur dioxide (SO2) per MW generated lower, than the existing East 1 facility. The new plant will include low-NOx emissions, an electrostatic precipitator to control the emissions of particulate matter and a flue gas desulphurization (FGD) system to control emissions of SO2. The low-NOx burners will limit NOx emissions to no more than 200 mg/Nm3 (dry 6 per cent CO2). A post-combustion de-NOx system is unnecessary, which has the environmental advantage of requiring no storage of ammonia.


Partial view of the Maritza East 1 with the turbine hall in the foreground:
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Induced draught fans will draw flue gas exhaust from each boiler unit through an air heater, or heat exchanger, and into a set of electrostatic precipitators (ESPs). The ESP design allows the capture of fly ash and dust particles in the exhaust gas, which ensures compliance with World Bank and Bulgarian guidelines on particulate matter. Bulgarian environmental standards mirror the EU Directive, but additionally include a limitation on particulate emissions under 2.5 µm that is yet to be included in the EU Directive. The combined effect of the ESP and downstream wet FGD will limit dust emissions at the stack to 30 mg/Nm3 (dry 6 per cent CO2) or less.

Flue gas will pass from the ESPs into the wet FGD system. This will absorb sufficient SO2 to ensure compliance with World Bank, EU and Bulgarian SO2 emission guidelines. Desulphurized gas from each of the 335 MW units will pass into the atmosphere through individual flues that the main cooling tower will house. Each flue will employ equipment for continuous emissions monitoring of SO2, NOx and particulates. The plants at Maritza East 2 are smaller and fail to meet the guidelines on emissions, as does another plant that will either have to retrofit abatement technology in the next few years or face the prospect of operating for only limited hours and eventual closure after 2008.

The wet FGD system is designed for an SO2 inlet concentration of up to 21 890 mg/Nm3 (dry 6 per cent CO2), equivalent to a maximum sulphur content in the lignite of 2.7 per cent. Under the above conditions, the SO2 outlet concentration will not exceed 400 mg/Nm3 (dry 6 per cent CO2).

The wet FGD absorber is designed for a chlorides concentration of 22 500 ppm, with material selected to resist to a concentration of 350 000 ppm to provide an adequate safety margin. To control chlorides, the system will operate at a fixed blow-down flow-rate with floating chloride concentration. The flow from each absorber is around 10 m3/h. There are seven absorber spray levels. At guaranteed conditions, six of these will be in operation, all seven at design conditions.

To secure the required level of performance in terms of SO2 removal and at the same time minimize the power consumption of the wet FGD installation by selecting the lowest possible liquid-to-gas (L/G) ratio — and also balancing all the other process parameters to a global optimum — the absorber vessel will employ ‘performance-enhancement’ plates. These are radial baffles that will project inward from the spray tower wall to redirect flue gas back into the spray zone if any has bypassed the spray nozzles by travelling up the wall. Performance-enhancement plates can substantially improve the efficiency of removal of SO2 — by 2-5 per cent — or, conversely, substantially reduce L/G ratio by 10-20 per cent. This provides savings in capital and operating costs.

Since the system has no flue gas bypass, an emergency quench system will cool the flue gases if abnormal conditions occur such as failure of the air preheater or non-operation of the recycle pump. Gypsum by-product will simply go into landfill. Its residual moisture content will be 15 per cent.

The existing Maritza East 1 plant discharges heated cooling water into the Rozov Kladenetz Lake and storm water and wastewater to an existing ash pond. The new facility, however, will have zero discharge of wastewater, which was quite a challenge in technical terms.

A natural draught cooling tower that is partially fed by process water will cool the condenser. This recycling of water will significantly reduce the amount of water taken from the lake. In addition, cooling tower blow-down and other potential facility discharges such as boiler blow-down, plant drains and demineralization system reject water will be used within the wet limestone FGD system. The wet FGD is in fact designed to use the blow-down from the main cooling tower as make-up water, thus reducing the total water consumption of the installation. The blow-down will also moisten fly ash.

During operation, the pump station that serves the existing Maritza East 1 plant will draw water for the new plant from the lake. As a zero-discharge facility, wastewater will be recycled and reused within the facility. There will be no discharge of wastewater to local surface water, and therefore none of the impacts associated with wastewater discharges.

Consideration has also been given to noise levels both within the installation and in the surrounding area. Most of the equipment – including the limestone crushers, ball mills, recycling pumps and oxidation blowers — is enclosed within a building. Also, the ID fans have discharge silencers to limit noise emission from the stack, and the cooling tower itself is at the rear side of the property to maximize the distance from external receptors.

Tight schedule

Alstom is building the new power station just over 36 months, which will be a world record for this type of plant. To achieve this, the company has adopted an aggressive policy from the beginning of the project. For example, pre-engineering allowed it to order and deliver parts much earlier than usual, effectively as soon as the contract was signed.


Delivery of the stator for the second generator
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The plant is in the construction phase, with civil works 80 per cent complete. The boiler steel structure is nearing completion, and work has begun on pressure parts. The steam turbines are now on site and are being placed on their foundations.

The biggest challenge has been during this construction phase. Bulgaria has built no new power plants in the past 20 years, which made finding skilled labour and knowledge in the country a difficult task. Alstom decided to use Turkish contractors to manage construction with the help of German workers.

In April this year, the project entered its 20th month, putting it at about 65 per cent complete. Unit 1 will begin operation in May 2009 and Unit 2 three months later.

Showcase

Investors are watching this showcase project to gauge whether other IPP schemes can be completed on time in Bulgaria despite the labour challenges the country faces. The project already has high standards concerning health and safety — quite an accomplishment in a country that has no culture in this aspect of project engineering. To achieve this, Alstom opened a school in which experienced workers from Europe trained local workers in health and safety issues related to construction. These students received certification diplomas on satisfactory completion of the training programmes.

The old Maritza unit will close in 2009. As other old generating facilities in Bulgaria follow suit, the new Maritza plant will help the country meet its overall national objectives for additional power generation. It will also secure the long-term future of the lignite mine and limestone quarry operations and help to further the deregulation and privatization of the country’s power sector.