Constructing China’s largest supercritical power station

The Suijun coal-fired power plant (Figure 1) is being built in Liaoning province in north east China at Liao Dun Gulf on the Yellow Sea. The contract for the plant is between the Russian state organisation Technopromexport and the China National Technical Import & Export Corporation, Technoimport.

The Suijan plant, which uses supercritical steam conditions, has been designed by OAO Teploelectroproject, the Russian Design Institute for Power Engineering. Suijun’s total rated capacity will be 3200 MWe. The first phase of two 800 MWe supercritical units has already been completed.

The supercritical pressure (24 MPa) reduces specific heat consumption per kWh to 9378 kJ/kWh. This figure represents a significant improvement compared with units operating at pressures of 18 MPa and 13.8 MPa, namely 2.5 and 3 per cent respectively.

The design was based on experience of supercritical units in Russia, including those with sliding pressure operation.

Synchronisation of Suijun unit 1 with the Chinese grid took place in December 1999. Unit 1 will be put into trial operation in June 2000, and commissioning of Unit 2 is planned for September 2000.

Main components

Suijun has once-through boiler (Figure 2), which were manufactured by the Krasnyi Kotelchik boiler works in Taganrog, Russia. The boilers will fire Chinese coal from Dinbay coal field.

Boiler

The technical data for the boilers are as follows:

Live steam generating capacity 2650 t/h

Live steam outlet pressure 25 MPa

Live steam temperature 545°C

Feedwater temperature 277°C

Reheat steam capacity 2152 t/h

Reheat steam temperature 545°C

Reheat steam pressure 3.9 MPa

Boiler unit efficiency 92.3%

Slag removal Dry bottom

Service life 40 years.

Each boiler is a suspension-type boiler with a T-shape layout. In designing the boiler, special attention was paid to ensure slag-free operation. Rows of swirl burners (12 burners per row) were arranged on the side-walls of the furnace with a special flue-gas recirculation system, limiting the flue-gas furnace outlet temperature to 1050°C.

The boiler is fitted with an individual direct-fired system. The boiler has eight roller mills, arranged such that the pulverised coal from each mill feeds 6 burners arranged on the furnace side-walls in one row.

Due to high fuel ash abrasiveness, the velocity of the flue gas in the superheater horizontal convection section is limited to 7 m/s.

To control the outlet steam temperature, spray-type coolers are used while reheat steam temperature is controlled by steam-to-steam heat exchangers.

The boilers have devices to clean slag and ash deposits from heating surfaces. They also employ starting dump separators and 14 m diameter regenerative air-heaters. The weight of one boiler unit is about 15 000 t.

Turbine

The turbine units for Suijun were designed and manufactured by the Leningrad Metal Works. The condenser-type turbines use steam reheating, and have a capacity of 800 MWe at the rated steam pressure in the IP cylinder of 3.5 MPa, 540°C and 3000 rpm.

The turbine is a single-shaft, five-cylinder unit, comprising one HP cylinder, one IP cylinder and three LP cylinders. The unit is designed for base load operation.

Main turbine technical data are as follows:

Turbine length without

generator 39.5 m

Turbine length with generator 59.5 m

Turbine weight without

condensers, auxiliary

equipment and pipelines 1308 t

HP rotor Integral design

IP rotor Integral design

LP rotors Shrunk-on discs

Height of last stage LP blades 960 mm.

The turbine unit has 8 non control steam bleeds for regenerative heating of the full-flow condensate in four LP heaters and in the deaerating section, and for heating the feedwater in three HP heaters. Steam bleed is also required for turbine-driven feed pumps.

Condensers

The turbine has a condenser unit consisting of two series-connected condensers and three water-jet ejectors. The condensers are designed to use sea water.

The condensing unit comprises two lengthwise condensers with identical cooling surfaces. The cooling water passes consecutively through the condensers in two parallel flows, thus making it possible to shut off one of them without stopping the turbine.

The main condenser technical data are:

Total cooling area 41 200 m2

Tube diameter 28 mm

Tube thickness 1 mm

Tube length 12 000mm

Water consumption 80 000 m3/h.

Generators

The generators for Suijun were designed and manufactured by Electrosila of Russia.

The generator technical data are:

Output 800 MWe

Nominal voltage 24 kV

Power factor 0.9

Stator winding

cooling Direct water

Rotor winding

cooling hydrogen.

Transformers

The step-up transformers for Suijun were produced by Zaporozhtransformator in the Ukraine. They are three-phase, two-winding, power transformers with directional forced oil injection into the transformer winding and controlled water and oil circulation in the cooling system.

The transformer nominal voltage is 525/24 kV, with a rated capacity of 1000 MVa.

Power from Suijun phase 1 will be transmitted into the Chinese grid at 220 kV and 500 kV through two 220 kV and two 500 kV transmission lines.

Fuel supply

The boilers are designed to fire bituminous coal with moisture content of 9.6 per cent, ash content of 19.8 per cent, and volatile material content of 32.3 per cent, and low calorific value 22.4 MJ/kg. Suijun is about 700 km from the coal field. The coal is brought to the Suijun fuel storage area by railway and the coal storage yard can store 460 000 t of coal.

Coal is transported to the main building by belt conveyor. The main coal storage facilities have two rotor-driven stackers of 1200 t/h and pick-up loaders of 1500 t/h. A special system is provided to automatically load the boiler silos. Diesel fuel of calorific value 41.0 MJ/kg is used to start the boilers. The diesel fuel is stored in three tanks of 3000 m3 volume each.

Cooling system

Individual cooling of the main equipment of each plant is provided at Suijun. The design will ensure autonomous operation of each unit and help achieve reliable operation of the whole system. It will simplify maintenance and servicing due to the smaller number of control and shut-off valves. Circulating water used to cool each unit will be fed in two flows via the circulating pump, feed pipelines and condenser.

Sea water from the gulf is used as a service water source. A single discharge channel is built to service two units.

At full load 179 000 m3 of water is consumed by the two units. The temperature drop of the discharged circulation water will be 9.4°C. To prevent biological fouling caused by the inner of the water pipelines being in direct contact with sea water, special thermal treatment of the service water is carried out, involving heating the water to 40-50°C. The station and auxiliary equipment is cooled by fresh water. This water is recycled through cooling towers.

Ash and slag disposal

A single reinforced concrete monolithic stack was erected for the two units. The 270 m high stack has two 7.2 m dia. steel ducts (one for each boiler).

To trap and collect the fly-ash, three electrostatic precipitators are installed for each unit. Ash collection efficiency is 99 per cent. Double-stage ash handling pumps pump the ash from the ash collectors to the ash removal area, 7.5 km from Suijun. Slurry from the boiler slag tank flows by gravity to the slag-pumping house. The maximum slag flow rate from one boiler is 15.5 t/h. Fifty per cent of the purified water (out of the total slag slurry fed to the removal area) is recycled.

Control system

Teleperm XP-R (Russia) processors are used to provide automated control. This equipment was designed and manufactured by Interavtomatika, a joint venture of Siemens, the All-Russian Thermal Engineering Institute (VTI) and Technopromexport. Teleperm XP-R is a distributed microprocessor-based system. The low-level controllers are the latest analogue version of the Teleperm XP-R, manufactured under the Siemens licence.

The unit process control system has some 2000 inputs and controls the 850 gate valves, 155 control valves and 425 motors and solenoid valves.

The main automatic control board supervises and controls the power plant’s performance under every mode of operation. The system incorporates 200 protections, 2000 interlocks, boiler step-by-step logic control, including burner management and turbine start-stop control.

For direct-fired boilers, the fully automated firing process is especially important. The three-level scheme of regulating the process of firing is as follows: mills (coal supply, primary air supply), firing (secondary fuel and air supply), temperature correction for the supplied fuel.

The whole project has a relatively high level of automation, with TV screens as the basic method of interfacing operator activities in all normal operational modes.

An auxiliary control panel is provided for emergencies, including shut-off of the main or auxiliary equipment.

Experience with the process control accumulated in operating unit 1 confirmed the claimed advantages of the hardware (reliability, dynamics, easy debugging and servicing).

Layout of the main building

The main building is a 9-bay structure. It is 246.6 m long and houses the following: bunker, deaerating unit, transfer towers, boiler room, turbine room and facilities for electrical equipment. The overall building height is 117 m.

Layout of the main components is determined by the T-shape layout of the boiler unit design. The boiler is suspended by beams, resting on the columns of the boiler room. The equipment in the turbine room is arranged lengthwise with the turbine axis placed along the turbine room. The turbine cell is displaced by 2 bays (each bay 12 m long) from the boiler cell, allowing the HP cylinder to be placed opposite the boiler axis. This layout optimises the arrangement of main pipelines and minimises the pressure drop, especially in the preheat system. The turbine, generator, auxiliary equipment, regenerative feed water heating, service water heaters and other equipment are in the turbine cell.

The basement of the turbine room accommodates cable-ducts, circulating pipelines, service water-supply system, closed-circuit collector system, water pipe network for ash and slag sluicing, and drainage pipe lines.

Erection of metal works

The erection and civil works at Suijun were mainly carried out by local civil engineering subcontractors of the North-Eastern Electricity Board of China in Shenjang, Liaoning province. Supervisors from Beijing State Civil Engineering Commission oversee the quality of the design documentation and equipment, and progress in the civil and erection works. The Commission also co-ordinated the subcontractors’ activities with those of Technopromexport. Experts from Technopromexport are responsible for design, inspection, erection and supervision of commissioning works on Suijun.

To improve quality and productivity in the erection of the main building, preassembled large blocks of up to 85 t (Figure 3) were used. These were assembled at special stands. 95 t and 75 t travelling gantry cranes and 40 t crawler-type cranes were used in erection, making possible simultaneous crosswise assembly of the main building. Column end-butts and tie-beam joints were fixed together through sand-blasted fitting flanges by high-tensile bolts. These bolts are only used to fix basic assembly joints. Secondary assembly joints are fixed by normal bolts and later secured by welding.

The erection of tie-beam framework and roofing for the boiler units was carried out at the same time as assembly of main boiler equipment. The total weight of metal in the main building and auxiliary facilities for one unit is 62 850 t.

The technology used to erect and assemble equipment allowed the maximum scope of works to be carried out at the assembly sites. The boiler components to be mounted were arranged strictly following the order of the assembly schedule. A test assembly of the boiler unit was made at the assembly site to ensure that over-sized boiler components did not interfere with the assembly of the later-stage boiler parts and the parts adjoining them.

There were 407 pieces with a total weight of 10 558 tons per unit at the erection site. The assembled blocks were loaded onto the transport using specially arranged gantry cranes fitted with traverse sets.

The assemblies were introduced to the boiler room through 17.2 x 16 m temporary end-face wall-openings. Erection of the boiler units and arrangement of pulverised coal, flue gas and air ducts, as well as assembly of metalwork was by step-by-step assembly of large blocks (Figure 4).

Two 250 t special-purpose double-trolley overhead cranes were the main hoisting mechanisms for assembly in the boiler room. To rotate the assembled items from the horizontal to the vertical position 120 t upending devices were used (Figure 5).

Co-ordination of assembly, transport and erection were carried out by the central dispatching service of the Suijun erection division. The assembly of boiler equipment for unit 1 took 24 months. Once completed, trial operation could begin.

Transport of heavy equipment

The heavy items were transported to the construction site by railway. Heavy equipment was brought by sea to the Chinese port of Singan from St. Petersburg via the Ukrainian port of Ilyichevsk. This equipment included:

Unit transformers (465 t)

Generator stators (377 t)

HP heaters (126 - 172 t)

Station auxiliary power transformers (93 t).

Special railway transporters were provided to carry this equipment to the port (Figure 6). Gantry cranes at the port and cranes available on the chartered ships were used to handle and unload heavy items of equipment.

Initial operating experience with Suijun unit 1 has confirmed the merit of the design and high quality of the installed equipment.