Full steam ahead

Modernizing the Dolna Odra power plant complex – one of the largest generators in Poland – is a major undertaking. But the rewards, which include improved competitiveness, reduced emissions and reduced maintenance costs, will be worth the wait.

Jacek Czerwonka, Alstom Power, Elblag, Poland

Poland’s Dolna Odra power plant complex consists of three establishments: the Dolna Odra power plant in Nowe Czarnowo near Gryfino, and the Pomorzany and Szczecin power plants in Szczecin. This complex is one of the biggest manufacturers of electricity and thermal energy in the country. With a capacity of 1957 MWe and 750 MWt, it is ranked as the fifth biggest industrial energy manufacturer and the sixth biggest thermal energy manufacturer, with a six per cent share in the Polish power market.

Dolna Odra is a conventional multiple unit power plant. Its individual power units became operational during 1974-77 and it has a capacity of 1742 MWe and 100 MWt. The facility is fairly modern; the technology applied there, including highly efficient electro-filters, desulphurisation combustors and sewage treatment plants, ensures compliance with current environmental protection standards.

The Pomorzany power plant in Szczecin was built between 1936 and 1940, and recommissioned in 1961. With an electric power capacity of 127 MW, and a thermal capacity of 430 MW, the plant comprises two modernized power units, which use a unique simultaneous electron beam acceleration fumes desulphurisation and decarbonisation system based on Polish scientific research and Japanese technology.

Figure 1. Polish companies provided the majority of the equipment for the Dolna Odra complex
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The Szczecin plant has been operating since 1913, and was modernized in the 1950s. During the 1990s the burners of two Pauker boilers were replaced by their low-emission counterparts and modern electro-filters were installed. It has a capacity of 88 MWe and 220 MWt.

Ageing units

Over a period of almost 25 years, units 7 and 8 have operated for about 170 000 hours and performed about 900 start-ups. After this lengthy operation the turbine casings showed cracks, lowered impact resistance and tendency for plastic strains, which resulted in limiting the maximum allowable gradients of temperature increase to 2à‚°C/min. Moreover, the technical condition of the HP and IP steam paths showed an immediate need for replacement of diaphragms and the HP and IP rotor blades. During the overhauls carried out to date, the HP and IP rotor blades and the HP and IP diaphragms were replaced. In 1999, the HP and IP casings were repaired. In that same year, the turbine control system was modernized by application of the Electro Hydraulic Control System (EHCS) with a separate hydraulic power supply system together with individual control of HP control valves. The servomotors of the IP control and stop valves were also modernized. The steam dump system to the condensers were modernized and the carbon steel oil pipelines were replaced with stainless steel. Both turbines have modernized LP cylinders.

The life limiting components of these turbines are the inner and outer casings, together with integral valve chests, as well as the HP and IP rotors. After turbine unit operation of more than 200 000 hours, these components were at the end of their design life.

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To optimize the scope of modernization, Alstom carried out various technical and economic analyses. Calculations were made during the course of a year before and after the modernization, comparing the performance of the unit at the same electric power and availability level. Profits result from lower coal consumption by a turbine set. The calculations encompass avoided costs of the turbine life regeneration in 2005 and a general overhaul in 2010. However, the stress was put on the search for the best investment solution.

The high cost-effectiveness of the HP and IP cylinder modernization of the 13K215 turbine results from an improvement in thermal performance, including a decrease in unit heat rate and the possibility of achieving an electric power output of >230 MW as well as the avoided expense of repairs, unavoidable without modernization.

As a result of the forecasted technical condition, retrofits of the HP and IP cylinders allow the customer to achieve the following goals:

  • Turbine life extension
  • Increase in turbine reliability and availability
  • Extension of the intervals between overhauls of the HP and IP cylinders
  • Improvement in operational flexibility
  • Removal of the existing pressure limit in the HP control wheel chamber
  • Faster turbine start-up
  • Eliminating forced outages.

Alstom tendered a complex solution, proposing the supply of a new HP inner cylinder with modern technology reaction blading along with hydraulic power supply systems and servomotors. It was decided to preserve as much of the existing foundation as possible. The proposal included the supply of a new IP cylinder with the modern reaction blading, along with hydraulic power supply systems, servomotors, HP/IP pedestal and the LP stop valves.

The investment

In January 2004, the Dolna Odra power plant complex signed a contract with Alstom Power for the modernization of units 7 and 8. The contract comprises the replacement of the original HP and IP cylinders of the 13K215 turbine and their replacement with the new components, incorporating modern technology, offering higher efficiency and improved operational flexibility.

The installation commenced on March 1, 2005 when unit 8 was shut down. The initial operations focused on disassembling the existing equipment and making the necessary foundation modifications.

Figure 2. Work on Unit 8 was complete in July 2005
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The casings were replaced simultaneously with the bearing pedestals. In the place of the front pedestal, a VLH type bearing pedestal was used and in the place of the HP-IP pedestal, an ALM type pedestal was used. Additionally, a minor modification of the upper foundation plate was made within the IP cylinder area with regard to the new IP steam pipework.

As a result of the compact design (including the integrated valve chest) the HP turbine part was delivered to the erection site completely assembled. It was only necessary to weld in two flanges to the live steam pipeline delivered with the turbine and to attach steam sealing system pipework to the turbine and valve chest. The replacement of the HP turbine cylinder resulted in the following changes in the system:

  • Main steam pipework to the HP cylinder and cold reheat steam pipework from the HP exhaust to the reheater
  • Extraction pipeline system to the XW2, XW3 feed water heaters
  • HP cylinder drains pipework
  • HP outlet cold reheat non-return valves.

During the disassembly of the HP part the following parts of the old turbine were removed:

  • Steam chests with HP stop valves
  • HP casing and HP control valve chests
  • Steam pipelines between the HP stop valve chests and the HP turbine cylinder
  • Section of the cold reheat pipework from the HP cylinder.

The steam pipelines were installed and adapted to the configuration of the new HP cylinder. During the replacement of the HP cylinder the heating system for the intercasing space was also removed.

The new configuration of the steam pipelines to the HP cylinder made it necessary to modify the drains system pipework. The pipelines and the fittings were replaced by their new counterparts in the section between the HP parts and expanders. Because of the replacement of the HP cylinder and the new power supply system, the gland sealing system was also modified.

The modernization of the drainage system involved replacement of five DN350 expanding pipelines by two expanders placed symmetrically on the both sides of the turbine set. One of the expanders is a high-temperature model, the other collects the drainages of lower temperatures. The drainage system had been designed to make the changes in the drainage pipelines routes as small as possible.

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The crucial element of the retrofit of the IP cylinder was the replacement of the complete IP cylinder along with the hydraulic power supply system. The design of the IP cylinder incorporates the latest steam turbine technology. The new IP cylinder has a spiral steam inlet providing the optimum way to transfer the steam to the blading and the latest technology high efficiency steam turbine blading.

As in the case of the HP cylinder, the IP cylinder replacement required the following changes in the installation of the hot reheat steam pipework to the IP cylinder, the extraction pipework connections to the IP cylinder and the drainage system.

Disassembly work of the IP part, apart from the casing, comprised:

  • IP valve chests
  • Steam pipelines between IP stop and control valve chests at the turbine
  • Sections of steam pipelines before IP stop valve chests
  • Sections of extraction pipelines at the extraction stub pipes on the IP casing.

As a replacement the following were installed:

  • New valve chests
  • Steam pipelines at the inlet to valve chests
  • Extraction pipelines to the new locations of the extraction stub pipes on the IP turbine casing.

The new configuration of the steam pipelines in the IP cylinder made it necessary to introduce changes to the drainage system pipelines. Similar to the HP cylinder drains, the existing fittings had been used and the pipelines were replaced only in the section from IP cylinder to the expanders. As a result of the replacement of the existing IP cylinder, the gland sealing system was also modified.

Warranty measurement tests were performed in August. Measurement was done for specific heat rate consumption for four different guaranteed load points. Also maximum power output, dynamic state performance and noise level were measured. All results of the warranty tests confirmed that all guaranteed parameters were fulfilled and that the objectives of the project were achieved.

As a result of a new investment plan, Dolna Odra amended its contract with Alstom. Unit 7 will now be modernized in 2007, while in 2006 work will be carried out on unit 2. Site Works started on 1 April and will be completed in August.

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