A 3-year PhD position on the above mentioned topic is open. The project will be conducted as a collaboration of the CHEC (Combustion and Harmful Emission Control) Research Centre, Department of Chemical Engineering and the Risø Biomass Gasification Group. Both at the Technical University of Denmark.
Supervisors: Associate Professor Peter Arendt Jensen (paj@kt.dtu.dk), Professor Peter Glarborg (pgl@kt.dtu.dk), Associate Professor Ulrik Birk Henriksen, (ubh@mek.dtu.dk).
Background
A main feature of the LT-CFB process (Low Temperature Circulating Fluidized Bed process) is that it can handle fuels with high alkali content. The concept makes it possible to convert a biomass fuel to a gas that can be utilized in a power plant boiler, while the biomass fuel ash mainly is separated from the gas by the LT-CFB system. The heating value from the biomass is delivered to the boiler and problems with ash deposit formation and corrosion are prevented, that may arise if the solid biomass is utilized directly in the boiler. To insure optimal operation of the LT-CFB plant it is important to have careful control of the local operation conditions, and thereby control of the ash behavior in the system. It is important that the gas delivered to the boiler has a low alkali content, and at the same time de-fluidization caused by agglomeration shall be prevented.
The LT-CFB concept is based on the combined operation of two Fluid bed reactors. In one reactor a low temperature combustion and gasification of the biomass char is done which supplies the process energy. In the other reactor the biomass is pyrolysed whereby gas and tar are released. The supply of steam and the applied reactor temperatures are a careful compromise between ash related problems and optimal reactor operation. Using too low a temperature causes a decreased capacity and a poor carbon conversion. Using too high temperatures may cause de-fluidization and alkali gas phase release. To assist the further development and optimization of the LT-CFB concept it will be an advantage to obtain more fundamental knowledge on biomass ash behavior in the LT-CFB concept.
Studies on ash behavior in fluid beds have previously been performed, however, only very limited work are available on using high alkali fuels as straw. A lot of studies have been conducted on alkali release and transformation in combustion systems while alkali transformation in a low temperature gasification reactor is less known. The proposed PhD study will deal with the biomass ash behavior in the Low Temperature Circulating Fluid Bed gasifier.
Project content
The PhD project will be co-supervised by the Biomass Gasification Group (DTU-Risø) and the Department of Chemical Engineering (DTU). The Ph.D. student will participate in some of the experiments conducted at a large DONG Energy owned LT-CFB pilot plant, as well as perform studies in the laboratory using small scale equipment. The student work will be supported by experienced technicians and senior scientific personal.
To support the development of the LT-CFB concept and get a better understanding of the ash behavior and ash chemistry in the reactors the PhD study will mainly focus on the following subjects:
- The release, binding and transformation of alkali, chlorine and sulfur in low temperature gasification and pyrolysis reactors, and detailed concentration analysis of the ash forming elements in the CFB exit gas as function of reactor operation.
- The interaction of the ash with bed material and study of the Influence of process and fuel properties on possible de-fluidization.
It is the objective to provide recommendations on which reactor conditions and fuel compositions that will cause ash species release to the boiler and at which conditions de-fluidization will take place. If time is available and the measuring results can be used for it the following subjects will also be included in the study:
- Characterization of residual products with respect to optimal utilization.
- Study of overall steady state bed chemistry and the need for bed management.
- Study on the influence of the Cl rich CFB exit gas on boiler operation.
The PhD project work will be initiated by a literature study and a detailed analysis of the experiments that previously has been conducted on the LT-CFB test rigs. Further work will mainly be done on different size laboratory test rigs available at the Biomass Gasification Group (DTU-Risø) and the Department of Chemical Engineering (DTU). These include the 100 kW LT-CFB, a laboratory fluid bed test rig for de-fluidization studies and a laboratory ash release oven. Data from the DONG Energy owned 6 MW pilot plant LT-CFB will mainly be utilized in terms of analysis of collected ash and bed samples.
Practical information
Expected period for the PhD study is summer 2010 to summer 2013.
The PhD project will be conducted in a collaboration with the companies DONG Energy A/S (Rasmus Glar Nielsen) and Danish Fluid Bed Technology (Peder Stoholm).
The salary and appointment terms are consistent with the current rules for PhD degree students at the Technical University of Denmark: http://www.dtu.dk/English/education/Phd_Education.aspx.
Approval and Enrolment
The scholarships for the PhD degree are subject to academic approval, and the candidates will be enrolled in one of the general degree programmes of DTU. For information about the general requirements for enrolment and the general planning of the scholarship studies, please see the DTU PhD Guide.
Contents of PhD application and application procedure
Candidates should hold a master degree in chemical engineering, or similar degree with an equivalent academic level. Applications must include Curriculum Vitae, a statement on your motivation for applying, recommendations, and copies of all grade lists and other relevant diplomas.
We must have your online application by 3 August 2010. Please open the link “apply for this job online” and fill in the application form and attach the above mentioned documents.
All interested candidates irrespective of age, gender, race, religion or ethnic background are encouraged to apply.
Further information
Further information about the project may also be obtained from the supervisors. Further general information regarding Ph.D. studies at DTU is available at:
Technical University of Denmark: www.dtu.dk
Department of Chemical Engineering: www.kt.dtu.dk
CHEC Research Centre: www.chec.kt.dtu.dk
