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Externally fired gas turbine cycle based on biomass gasification gas as fuel
KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Energy services are essential for the development of societies, reduce poverty, and improve the living standards of inhabitants. The conventional routes to provide energy services employ fossil fuels. However, this involves environmental and availability concerns. Environmental issues and the need for energy security demand the use of alternative energy sources. Biomass is a renewable energy source that is advantageous because of its dispatchability and local availability worldwide. Local generation at small scales is interesting because it reduces energy losses when transporting electricity and heat. The development of sustainable decentralized small scale heat and power plants (CHP) using biomass is thus important.

In this context, this work is mainly focused on the development of an energy conversion technology based on an externally fired gas turbine using biomass gasification gas as fuel. Although this system is not new, its applicability with biomass gasification gas has not been widely studied. This work is divided in three parts. In the first part, the effect of the fuel composition and fuel inlet temperature on the performance of an externally fired gas turbine prototype is analyzed through simulations. Then, the performances of two types of heat exchangers are compared under the operational conditions of the prototype taking into account different thicknesses of deposit materials. The results shows that the composition of the fuels and the corresponding flue gas temperatures affect the electrical power output of the system. However, this is limited by the operating temperature of the heat exchanger. It is also reported that a decrease in the effectiveness of the heat exchanger has a greater influence on the electrical power output than an increase in the pressure drop as a result of deposit materials. High pressure drops in the hot side of the heat exchanger slightly affect the electrical power output. If biomass gasification gas is to be used after the gasifier with reduced cleaning steps, the effect of contaminants such as tar in the combustion performance is important. The last part in this work describes experimental studies of the effect of benzene as tar representative in the combustion performance of a surrogate mixture of biomass gasification gas. Polyaromatic hydrocarbons such as benzene, present in tar in biomass derived gas, affect the combustion emissions depending on their concentration in the fuel gas.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. , xxii, 122 p.
Series
TRITA-KRV, ISSN 1100-7990 ; 15:03
Keyword [en]
Externally fired micro gas turbine, heat transfer, combustion of biomass derived gas, micro combined heat and power
National Category
Engineering and Technology
Research subject
Energy Technology
Identifiers
URN: urn:nbn:se:kth:diva-165166ISBN: 978-91-7595-524-7 (print)OAI: oai:DiVA.org:kth-165166DiVA: diva2:807663
Public defence
2015-05-18, F3, Lindstedsvägen 26, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
Sida - Swedish International Development Cooperation Agency
Note

QC 20150424

Available from: 2015-04-24 Created: 2015-04-23 Last updated: 2015-04-24Bibliographically approved
List of papers
1. Effect of the fuel type on the performance of an externally fired micro gas turbine cycle
Open this publication in new window or tab >>Effect of the fuel type on the performance of an externally fired micro gas turbine cycle
2015 (English)In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 87, 150-160 p.Article in journal (Refereed) Published
Abstract [en]

Externally fired gas turbines open the possibility of using fuels of lower quality than conventional gas turbines and internal combustion engines. This is because in externally fired gas turbines, the flue gases heat the compressed air in a high temperature heat exchanger. This heat exchanger can more easily deal with contaminants present in the flue gases. In this regard, the configuration of externally fired gas turbines represents an interesting option for biomass gasification gas. The contaminants and low heating value (LHV) of this fuel have made it difficult to find a conversion technology for heat and power generation. For this reason, it is important to study the influence of biomass derived gas as fuel on the performance of this system and consider the effects of the contaminants in the high temperature heat exchanger. This is studied in this work through simulations using Aspen Plus and Matlab. The test data of an externally fired micro gas turbine prototype was used to validate the simulation. The fuel considered was biomass gasification gas with varying concentrations of benzene 100, 10 and 1 g/Nm3 (hereafter named m100, m10, and m1 respectively). Additionally, mixtures of biomass derived gas and methane were studied for 10 and 50% of the thermal power of the combustor. The fuel inlet temperature to the combustor varied from 150 °C to 750 °C in order to represent the fuel gas after removal of particles by a cyclone and a filter. The results showed that the electrical power output increases when high fuel inlet temperatures to the combustor are used. Additionally, although it would be expected that fuels with higher LHV (lower heating value) show higher temperatures and higher output power, this does not always occur because of the composition of the fuels and their respective flue gas temperatures. The addition of methane does not have a large effect on the electrical power output. For a fixed temperature limit in the heat exchanger, the composition of the fuels does not play an important role. However, high fuel inlet temperatures to the combustor show slightly higher efficiencies. Additionally, the effect on the electrical power output of increasing the pressure drop as a result of increased thickness of deposit materials in the heat exchanger was analyzed.

Keyword
Biomass derived gas, Electrical power output, Externally fired gas turbine, Flue gas temperature, Fuel inlet temperature, Lower heating value, Pressure drop
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-165263 (URN)10.1016/j.applthermaleng.2015.04.042 (DOI)000359504500016 ()2-s2.0-84930199023 (Scopus ID)
Note

QC 20150629. Updated from manuscript to article in journal.

Available from: 2015-04-24 Created: 2015-04-24 Last updated: 2017-12-04Bibliographically approved
2. Analysis of a high-temperature heat exchanger for an externally-fired micro gas turbine
Open this publication in new window or tab >>Analysis of a high-temperature heat exchanger for an externally-fired micro gas turbine
Show others...
2015 (English)In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 75, 410-420 p.Article in journal (Refereed) Published
Abstract [en]

The externally-fired gas turbine (EFGT) can convert fuels such as coal, biomass, biomass gasification gas and solar energy into electricity and heat. The combination of this technology with biomass gasification gas represents an interesting option for gasification, for which it has been difficult to find a conversion technology. In this system, the heat exchanger deals with the contaminants of biomass derived gas instead of the turbine itself. However, these contaminants can build a deposit layer in the heat exchanger that can affect its performance. The heat exchanger is important in externally fired gas turbines since the turbine inlet temperature is directly dependent on its performance. Several studies on heat exchangers for externally fired gas turbines have been carried out. However, very few detailed studies were found comparing the performance of heat exchangers for externally fired gas turbines considering the effect of deposit materials on the surfaces. In this regard, this work compares the performance of a corrugated plate heat exchanger and a two-tube-passes shell and tube heat exchanger considering the effect of thickness of deposit material with different thermal conductivities on pressure drop and effectiveness. The results show that the effectiveness of the corrugated plate heat exchanger is more influenced at larger thicknesses of deposit materials than the two-tube-passes shell and tube heat exchanger. There is an exponential increase in the pressure drop of the plate heat exchanger while a monotonic increase of pressure drop is seen for the shell and tube heat exchanger. The increase in the thickness of the deposit material has two effects. On one hand, it increases the resistance to heat transfer and on the other hand, it reduces the through flow area increasing the velocity and hence the heat transfer coefficient. Additionally, the effectiveness of the heat exchangers had a stronger influence on the power output than the pressure drop.

Keyword
Externally fired gas turbine, Heat exchanger, Biomass gasification gas, Deposit materials, Effectiveness, Pressure drop
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-159351 (URN)10.1016/j.applthermaleng.2014.10.014 (DOI)000347263800041 ()2-s2.0-84921464634 (Scopus ID)
Funder
Sida - Swedish International Development Cooperation Agency
Note

QC 20150202

Available from: 2015-02-02 Created: 2015-01-29 Last updated: 2017-12-05Bibliographically approved
3. Extended operability of a commercial air-staged burner using a synthetic mixture of biomass derived gas for application in an externally fired micro gas turbine
Open this publication in new window or tab >>Extended operability of a commercial air-staged burner using a synthetic mixture of biomass derived gas for application in an externally fired micro gas turbine
2015 (English)In: Fuel, ISSN 0016-2361, E-ISSN 1873-7153, Vol. 150, 664-671 p.Article in journal (Refereed) Published
Abstract [en]

Biomass gasification converts solid biomass into a gaseous fuel that is more versatile and can be used in many applications. However, biomass gasification gas contains some contaminants and inert compounds. The contaminants can cause several problems in the downstream equipment and undesirable emissions while the inert compounds can affect the lower heating value of the gas. Because of these characteristics, there have been difficulties in finding a conversion technology using biomass gasification gas for heat and power generation. In this regard, externally fired gas turbines open a possibility for this combustible gas since due to its configuration, combustion takes place outside the conventional gas turbine cycle. For this reason, combustion studies of biomass derived gas are important. In this work the operability of a commercial air-staged natural gas burner is shown in terms of CO, UHC, and NOX emissions using a synthetic mixture of biomass gasification gas. Two fuel gas mixtures simulating the composition of biomass gasification gas are injected in the combustor. Each fuel gas contains different injection rates of benzene in order to represent tars and to understand their effect on the combustion performance. Additionally, the equivalence ratio is varied in a range of lean conditions in order to find an optimum operation point for the burner studied. The results showed that the presence of polyaromatic hydrocarbons such as benzene reduced the CO concentrations in the exhaust gas while it increased the concentrations of unburned hydrocarbons (UHC) at equivalence ratios lower than 0.68. Additionally, NOX emissions showed a relatively constant trend over the range of equivalence ratios studied for both fuels. It was also observed that NOX emissions increase with the addition of benzene in the fuel gas. An optimum point with regards CO and UHC concentrations was found for the fuels tested.

National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-164411 (URN)10.1016/j.fuel.2015.02.048 (DOI)000351710400077 ()2-s2.0-84924322699 (Scopus ID)
Funder
Sida - Swedish International Development Cooperation Agency
Note

QC 20150424

Available from: 2015-04-24 Created: 2015-04-17 Last updated: 2017-12-04Bibliographically approved

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