Led by the chief engineer Weizhong Feng, engineers at the Waigaoqiao 3 coal fired power plant have been working hard and continuously on a series of innovations designed to substantially improve coal fired power plant performance, a package of measures they call the ‘5E technologies’: Energy saving; Efficiency preservation; Environmental protection; Ensuring safety; and Elevated turbine-generator.

Apart from the elevated turbine-generator concept, the other four measures have been applied successfully at Waigaoqiao 3, rendering it one of the most advanced high efficiency power plants in the world. Currently, the team is implementing the full portfolio of 5E technologies, this time including the elevated turbine-generator scheme, at the new 1350 MWe Pingshan Phase 2 ultrasupercritical coal-fired power plant, which employs double reheat.

The elevated turbine-generator idea, which could also be described as a split-level turbine generator, with elevated HP and IP1 (see below), was developed by Feng’s team to address problems with the conventional double reheat design. Technical evaluations indicated the new concept was feasible and would deliver economic benefits relative to the conventional configuration. Patents for have been granted in China, USA and EU.

The National Energy Administration (NEA) of China approved the technical evaluations and authorised a national demonstration project for the technology in 2015. It was initially planned to implement the new technology in a plant to be built next to the Waigaoqiao 3 power plant in the Shanghai region. However, the Shanghai government did not approve it due to its coal-control policy, so the project was relocated to Pingshan town in Anhui Province.

The project was given overall final approval on 28 December 2016 and construction started in 2017. As well as the elevated turbine-generator technology, the other 5E technologies, further improved since their deployment at Waigaoqiao 3, will also be implemented at Pingshan Phase 2. Upon commissioning, expected by the end of August 2020, Pingshan Phase 2 is likely to be the most efficient and cleanest coal-fired power plant in the world.

On 19 October 2018, accompanied by engineers from Feng’s team, Mr Li Li and Mr Zhang Jiancheng, I had the pleasure of visiting the Pingshan Phase 2 site and took the photographs below.

Older pulverised coal power plants operated at subcritical steam conditions and employed a single circuit of steam through a boiler and turbine. The single steam reheat loop and second reheat loop were introduced to increase the electrical efficiency. However, the reheat loops require additional boiler and turbine components, which raised capital costs. For a 1000 MW single reheat unit, the main and reheat steam pipelines can be as long as 200 m. In the double reheat system, the steam has to shuttle between the boiler and turbine twice, which further increases the flow resistance and heat losses. The steam in the pipe also increases the thermal inertia which slows the turbine load adjustment response. Furthermore, arranging these large diameter thick wall pipes within the plant building can pose difficulties.

Although the increased electrical efficiency and reduction in fuel consumption can offset the problems described, Feng’s team decided to radically rethink the double reheat pipework configuration to reduce heat loss and further improve efficiency. In the new arrangement, the elevated turbine-generator concept, also known as “cross compound with elevated and conventional layout”, the turbine-generator is split into two trains. One train, consisting of the HP turbine and IP1, with a generator, is elevated to around 80-85 m above ground level, and positioned near the top of the boiler, close to the outlets of the steam headers in the case of a tower type boiler. The other train, which consists of the IP2 and LP stages with a second generator, remains in the conventional position, roughly 17 m above ground level.

As shown by comparing Diagrams 1 and 2, raising the HP turbine to the level of the boiler steam header minimises the length of main steam pipe ➀ and cold reheat steam pipe ➁. By elevating the IP1 and HP casing, the hot reheat steam pipe I ➂ and the cold reheat steam pipe II ➃ are also minimised. The remaining hot reheat pipe II ➄ can also be shortened if needed.

The shorter pipework reduces the pressure drop and temperature loss of the steam, which increases efficiency and the cost of the piping is significantly cut.

The new concept will be implemented for the first time at Pingshan Phase 2. The basic layout is shown in Diagram 3.

The Pingshan Phase 2 turbine is being supplied by Shanghai Electric Corporation and Siemens, while the boiler (to be provided by Shanghai Electric and GE) will employ GE’s SteamH, its first ever application. 

A summary of main data for the Pingshan 2 steam turbine is shown in Table 1. The left hand column shows data for the initial Siemens design of double reheat steam turbine with Feng split level turbine- generator.

Supported by Siemens, Alstom (now GE) and the East China Electric Power Design Institute, the steam turbine design was further optimised by the Feng team and the data recalculated accordingly. This is shown in the right hand column of Table 1. Interestingly, the second reheat temperature was first re-estimated as 630°C but was changed to 623°C. It was realised that higher reheat temperature needed a larger boiler heat exchange area, which causes steam pressure to drop. At a lower temperature, the circulation efficiency is reduced but the boiler reheat area and resistance are also reduced. The overall efficiency is the same. However, using a lower temperature (623°C) heat exchanger saved the project about 40 million yuan RMB (almost US$5.8m).

As already noted, the other 5E concepts developed and used at Waigaoqiao 3 are also being fully implemented at Pingshan Phase 2. The scope of regeneration is for example widened significantly, expanding the regenerative cycle from a single feedwater- based system to the whole unit, including water, air and coal. Other measures include:

  • Low load operation improvement: To ensure steady combustion under low load, on the turbine side, the feedwater temperature is kept at the rated level by adding an adjustable valve on the extraction pipe to keep the outlet pressure unchanged. On the boiler side, low oxygen and low NOx combustion technologies are used over the whole load range. For auxiliary facilities, variable frequency power systems are applied extensively.
  • Load changing performance improvement: In order to respond quickly to grid operator requests, the governor valve of the turbine is generally throttled to retain a certain degree of thermal storage capacity. Changing the turbine load by a combination of condensate water frequency control and adjustable LP and HP steam extraction frequency control is employed to eliminate throttling losses.
  • SPE (solid particulate erosion) prevention: the approach successfully applied at Waogaoqiao 3 has been updated and will be employed at Pingshan Phase 2 to address the SPE problem.

One further potential improvement measure, seasonally adapted operation – in which the LP turbine is switched off in the summer – has been developed by the Feng team, but there are currently no plans to employ it at Pingshan Phase 2.

Although the double reheat system is being built with existing, mature, and well established 600°C materials and equipment, the Pingshan Phase 2 1350 MW unit is on its way to becoming possibly the most efficient coal-fired power plant in the world, at 49.8% (net, LHV). 

Acknowledgement: Author would like to thank Mr Li Li at Shanghai Waigaoqiao 3 power plant for facilitating the visit and technical advice.

References

W Feng and L Li (2017), China’s national demonstration coal power project achieves around 50% net efficiency with 600°C class materials, 8th IEA CCC Conference on Clean Coal Technologies, 8 – 11 May 2017, Cagliari, Sardinia, Italy

W Feng (2017), A high efficiency coal-fired power technology with elevated and conventional turbine layout, ASME 2017 Power Conference, 26–30 June 2017, Charlotte, NC, USA

J Mao and W Feng (2016), Innovative technology for double reheat USC, EPRI Asia Coal Power Technology Seminar, 6 September 2016, Tokyo, Japan

L Li (2018), personal communication (October and November 2018)