Ultra-Supercritical (USC) steam power generation technology with Circulating Fluidized Bed (CFB): Combustion, Materials and Modelling (USC-CFB-CMM)

Lead Research Organisation: University of Nottingham
Department Name: Faculty of Engineering

Abstract

To achieve the UK's ambitious target of reducing greenhouse gas emissions by 80% by 2050 without compromising energy security, the UK's conventional power plants must be operated in a flexible manner in terms of high efficiency, using alternative fuels (e.g. biomass) and integrating technologies for carbon abatement (e.g. Carbon Capture and Storage, CCS). Major reviews conducted by International Energy Agency in 2013 on the current status of the most advanced solid fuel-based conventional power generation technologies clearly show that ultra-supercritical (USC) steam Rankine cycle power generation combined with Circulating Fluidized Bed (CFB) combustion technology is the most viable alternative to the pulverised coal (PC)-based USC power generation. In addition, USC/CFB has a number of advantages over USC/PC, particularly regarding fuel flexibility.

However, there are still many fundamental research and technical challenges facing the development of USC-CFB technology. In particular, combustion issues related to safe and stable operation of CFB boilers when burning a variety of solid fuels are not yet fully understood and there is a great need to develop novel materials that will be able to cope with adverse conditions associated with USC/CFB operations.

This consortium brings together internationally recognised research experts from Universities of Leeds, Nottingham and Warwick in the fields of conventional power generation, fluidized bed combustion, power plant materials, modelling and control with the strong supports of industrial partners in Alstom, Doosan Babcock, Foster Wheeler and E.ON and its international academic partner - Tsinghua University. The project proposed aims to maximize the benefits of USC/CFB in terms of power generation efficiency, fuel flexibility including biomass and integration with CO2 capture by conducting research that addresses the key challenges in combustion, materials and modelling. The specific project objectives are:

(1) To understand how the combustion of a variety of fuels affects bed material agglomeration, fouling and corrosion of boiler heat exchanger tubes and emissions

(2) To understand the influence of the hostile conditions in USC/CFB in terms of creep and oxidation/corrosion resistance on ferritic, austenitic and Ni-based materials and to use the knowledge gained to develop coatings, enablng these materials to withstand the higher temperatures and pressures

(3) To investigate the additional impacts on combustion, emissions and materials when a USC/CFB is operating in the oxy-fuel combustion mode

(4) To develop a whole USC/CFB power plant dynamic model and to use the model to study optimal process operation strategies for higher efficiencies and better fuel flexibility

To achieve the proposed research aim and objectives and address the fundamental challenges, four inter-connected work packages composed of experimental and modelling studies will be completed:

(1) WP1 - Investigating CFB combustion issues through combustion tests at laboratory- and pilot-scales
(2) WP2 - Evaluating hostile conditions of USC/CFB on candidate materials
(3) WP3 - Development of surface engineered coatings & mechanical testing of coated alloys
(4) wp4 - USC/CFB system modelling

Planned Impact

Ultra-supercritical (USC) steam power generation combined with circulating fluidization (CFB) (USC/CFB) is the most viable alternative to USC/PC (pulverised coal) which represents the most advanced coal-power generation technology currently available to the conventional power generation industry. However, USC/CFB has a number of advantages over USC/PC, particularly regarding fuel flexibility. The proposed project has the potential to have a significant impact for the UK both in terms of Academic and industrial Impacts, and Economic and Societal Benefits. The potential impacts and benefits will be delivered by setting up a successful Partnership, maximising the benefits to the Users and Beneficiaries including the Trained Workforce on the project and establishing a range of effective Communication, Exploitation and Engagement Strategies.

The researchers trained through the project will provide high quality expertise for the power generation sector and its associated sectors in materials and modelling and control. Dozens of PhD students of the three partner universities working in the related research fields will be given opportunities to fully engage with the project teams, for example, through doing mini-projects alongside the employed PDRAs, attending research team meetings and consortium meetings, to enhance the academic impact at the partner universities.

The project will act as a catalyst for encouraging allied research and development of ultra-supercritical steam power generation, fluidized bed combustion, high temperature materials and coating, carbon capture and storage (CCS), and power plant system modelling. The successful outcome of this project, together with our current research portfolio of Conventional Power Generation, CCS, Power Plant Materials and Modelling will contribute to ensuring the UK can claim an international reputation in these research areas and thus encourage international students and researchers in the field to study in the UK. Know-how acquired in this project for USC/CFB will be of direct benefit to academics, conventional power generation, materials and CCS research communities, power generation, steel and energy industries, energy policy makers/regulators, and government departments such as DECC.

Successful delivery of the proposed research on USC/CFB will provide the UK with a platform to lead this new technology in the future, which will bring economic and societal benefits. There are many additional beneficiaries of the new technology in the long term including the public and industry who are the users of electricity.

The Project Consortium brings together strong research expertise in Power Plant Combustion Engineering, Chemical Engineering/Chemistry, Materials and Modelling, and the support from its industrial partners encompassing power plant technology developers and power generator. There are excellent links and proven working relationships between the project academic partners and the industrial partners.

Monthly local research team meetings, quarterly project consortium meetings and six-monthly Steering Committee meetings will be held to report research findings, to discuss any technical or management issues, and future research and implementation plans.

Knowledge Transfer Office of each partner university will liaise with industrial partners and other potential users of the developed IPs for commercial exploitation.

Findings with academic value will be disseminated at key international conferences and published with open access with the leading peer reviewed journals. We will host at least one workshop on Conventional Power Generation during the project period with the workshop fully open to the Conventional Power, Materials and CCS research communities and relevant industries. We will further disseminate the project results to national and international organisations and policy makers (e.g. DECC, Parliamentary Groups) through the established connections.

Publications

10 25 50

 
Description 1. Fluidised bed combustion tests with the laboratory-scale (20kWth) Bubbling Fluidized Bed (BFB) combustor under air and oxy-fuel combustion conditions: (a) Air staging can be very effective in reducing NOx emissions (up to 30%) for non-woody biomass fuels which usually have relatively high fuel-N content, especially if the secondary air is injected at the beginning of the freeboard zone of the BFB combustor and the BFB combustor is operated with a low overall excess air level. The use of air staging also leads to a significant decrease of CO emissions. (b) Replacing the air with an oxy-fuel oxidant implies a drastic decrease in CO emissions when burning biomass fuels in a BFB combustor (up to 80% reduction) when the oxygen concentration in the oxy-fuel oxidant is 30 vol. %, without increasing NOx emissions. (c) The addition of 1.5 wt. % (additive to biomass ratio) of lime to biomass fuels improves considerably the fluidization behaviour of the bed material allowing to work at higher temperatures (900°C) for longer time, due mainly to the increase of the Ca content in the biomass ash, leading to a low K-to-Ca ratios and increasing as a result the melting point of the eutectic K2O-CaO-SiO2. (d) The addition of a 5 wt. % (additive to bed material ratio) of dolomite or kaolin to the bed material allows to operate at higher bed temperature for much longer times due to: i) the capture of potassium species by forming potassium aluminium silicates with high melting temperatures (when adding kaolin); ii) the increase of the calcium content in the ash layer, increasing as a result the melting point of the eutectic K2O-CaO-SiO2 (when adding dolomite).
2. Fluidised bed combustion tests with the pilot-scale (100kWth) Bubbling Fluidized Bed (BFB) combustor under air combustion conditions: (a)Tests of three biomass fuels (white wood pellets, oat hull waste pellets, wheat straw pellets) were performed with a silica sand bed and it was found that white wood pellets had the best performance, for both extending operational time and a reduced accumulation of agglomerates, followed by oat hull waste pellets. Wheat straw pellets were significantly worse than both of these fuels, undergoing severe melt-induced agglomeration. (b) Different silica sand bed heights of between 7.5 in and 16 in were trialed at the pilot-scale. Tests showed that a smaller bed height lengthened defluidization time, implying improved vertical mixing at smaller bed heights. However, it was noted that a smaller bed height presented some operational issues in terms of maintaining the typical bed operating temperature (~850°C) whilst still using the desired amount of fuel. Additional heat removal capabilities would be needed to mitigate this. (c) Use of an olivine bed material had been trialed with a wheat straw fuel and compared against tests with a silica sand bed material, for operation at 50-60kWth. When using standard operational procedures including use of air pulsing, it was found that olivine would provide a significant increase in defluidization time (2-4 times). (d) Use of a finer/smaller particle size grade of olivine was found to further extend defluidization time when using a wheat straw fuel.
3. Development of surface engineered coatings & mechanical testing of coated alloys (a) Manufacture of thermally sprayed coatings using HVOF: 3 different types of coatings have been developed by HVOF thermal spraying and laser cladding for the corrosion protection of 304 stainless steel in a biomass boiler with high chlorine corrosive environment, which include: Ni-based coatings: NiAl; Co-based coatings: Stellite-6; and Composite coatings: MCrAlY/nano-Al2O3. The Ni-based coatings (NiAl) and Co-based coatings (Stellite-6) were tested in laboratory-scale @Nottingham, pilot-scale fluidized bed combustors @Sheffield and a commercial-scale coal-fired CFB boiler in China to investigate ash deposition as well as fireside erosion and corrosion. (b) Laboratory scale corrosion test in a simulated environment: the corrosion test of the coatings was completed with the outcome of 3 journal papers. (c) Mechanical creep testing Co-based stellite-6 coatings: the creep test of free-standing Co-based stellite-6 coatings was completed using 5 different loadings under three different temperatures and each test lasted over 1000 hours (40 days) and one journal paper on the small punch test of HVOF Stellite 6 Coatings - a comparative study of as-received vs post-heat treatment was published in Feb 2019.
4. CFB Power Plant Modelling (a) the classic zone method for the fluidized bed modelling has been developed and improved by incorporating radiative heat transfer between wall surfaces and gas volumes using in-house codes which can be applied to a wide range of industrial furnaces. The zone model is accordingly adapted in an efficient manner with process simulation in Aspen Plus, thus providing a more complete and flexible solution for optimizing the thermal performance of fluidized bed boilers. The main advantage of the proposed model stems from the thermal reciprocity within a combustor derived from the zone model which resolves the limitation of the sequential modular strategy in Aspen Plus. This novel modelling approach has been successfully demonstrated in the simulation of a laboratory scale atmospheric bubbling fluidized-bed combustor test rig. The predicted thermal performance and the reaction kinetics of the studied reactor are in good agreement with the experimental data. Relatively modest computing demand and acceptable accuracy make the developed model suitable to be incorporated into process simulations of a whole power plant. (b) The FluidBed module in Aspen Plus which can represent the realistic characteristics of a fluidized bed such as bubbling behavior and pressure drop was used for the first time to simulate an industrial 600 MW USC/CFB power plant system. Using this module made it possible to integrate the water wall heat exchanger and solid circulation based on specific elutriation models. A hierarchy-structured whole USC-CFB power plant model was constructed to investigate various flexible operational strategies. The operational data from an industrial scale 600MWe USC/CFB power plant were adapted to verify the developed model. Publications on the new modelling results are under preparation/review.
Exploitation Route The key findings had been discussed with the industrial partners at the regular project meetings, including the final project meeting at the end of the project. The industrial partners were best placed to consider the potential use of the findings at the earliest possible opportunities. Several conference presentations were made to disseminate the research findings to other interested academic researchers, industry and other stakeholders. A number of high quality journal publications have been published as open-access publications.
Sectors Agriculture, Food and Drink,Energy,Environment,Manufacturing, including Industrial Biotechology

 
Description The key findings had been discussed with the industrial partners at the regular project meetings, including the final project meeting at the end of project in 2018. Some of the industrial partners were interested in the key research findings. However, it is still too early to say how and when the industrial partners can use the key findings to their benefit. This is partly due to the uncertain future of the UK power generation industry with solid fuels. The key findings have also been presented to other stakeholders at several conferences presentations in order to maximize their potential use by other stakeholders. A number of high quality journal publications have been published as open-access publications.
First Year Of Impact 2016
Sector Agriculture, Food and Drink,Energy,Environment,Manufacturing, including Industrial Biotechology
Impact Types Societal,Economic

 
Description Project Kick-off meeting involving all industrial partners and academic partners, related researchers 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Industry/Business
Results and Impact About 20 people attended project formal kick-off meeting with all national/international industrial partners present.
There were formal presentations and discussions.
An Industrial Advisory Board was formally formed with the chair duly appointed.
Year(s) Of Engagement Activity 2015
 
Description Project meeting combined with an 'Energy Technology Research Institute' (ETRI) lecture on the Research and Development of Fluidized Bed Combustion Boilers in China 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Industry/Business
Results and Impact In total, about 35 people, comprised of those working on the project from the academic partners and industrial partners and other PhD students and researchers interested in the research attended the special ETRI lecture; it was a great opportunity to publicize the research project to other interested stakeholders; the ETRI lecture was delivered by a well-known international expert in fluidized bed combustion research, Prof Guangxi Yue, an academician of Chinese Academy of Engineering.
Year(s) Of Engagement Activity 2016
 
Description Project meeting with the participation of all academic partners and industrial partners as well as invited PhD students who are interested in the research 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Other audiences
Results and Impact A project meeting with the participation of all academic partners and industrial partners and research visitors (some of them are international)
Year(s) Of Engagement Activity 2018
 
Description Project meeting with the participation of all project partners and invited PhD researchers/visiting researchers 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Other audiences
Results and Impact A project meeting with the participation of all project partners and a number of PhD students and visiting researchers interested in the research - some of them are international.
Year(s) Of Engagement Activity 2017