Analysis of gas turbine systems for sustainable energy conversion

Increased energy demands and fear of global warming due tothe emission of greenhouse gases call for development of newefficient power generation systems with low or no carbondioxide(CO2) emissions. In this thesis, two different gasturbine power generation systems, which are designed with theseissues in mind, are theoretically investigated and analyzed.Inthe first gas turbine system, the fuel is combusted using ametal oxide as an oxidant instead of oxygen in the air. Thisprocess is known as Chemical Looping Combustion (CLC). CLC isclaimed to decrease combustion exergy destruction and increasethe power generation efficiency. Another advantage is thepossibility to separate CO2without a costly and energy demanding gasseparation process. The system analysis presented includescomputer-based simulations of CLC gas turbine systems withdifferent metal oxides as oxygen carriers and different fuels.An exergy analysis comparing the exergy destruction of the gasturbine system with CLC and conventional combustion is alsopresented. The results show that it is theoretically possibleto increase the power generation efficiency of a simple gasturbine system by introducing CLC. A combined gas/steam turbinecycle system with CLC is, however, estimated to reach a similarefficiency as the conventional combined cycle system. If thebenefit of easy and energy-efficient CO2separation is accounted for, a CLC combined cyclesystem has a potential to be favorable compared to a combinedcycle system with CO2separation. In the second investigation, a solid, CO2-neutral biomass fuel is used in a small-scaleexternally fired gas turbine system for cogeneration of powerand district heating. Both open and closed gas turbines withdifferent working fluids are simulated and analyzed regardingthermodynamic performance, equipment size, and economics. Theresults show that it is possible to reach high power generationefficiency and total (power-and-heat) efficiency with thesuggested system. The economic analysis reveals that the costof electricity from theEFGT plant is competitive with the moreconventional alternatives for biomass based cogeneration in thesame size range (<10 MWe). Keywords:power generation, Chemical Looping Combustion,CO2separation, oxygen carrier, biomass fuel, closedcycle gas turbine, externally fired gas turbineNR 2014080

Systems analysis of different value chains based on domestic forest biomass for the production of bio-SNG

This study compares value chains based on domestic forest biomass for the production of bio–synthetic natural gas (SNG) with respect to economic performance, GHG emissions, and energy efficiency. Value chains in which raw material is upgraded to intermediate products before transportation to an SNG plant integrated with a district heating system for further upgrading are compared with a chain in which the raw material is transported directly to the SNG plant. The intermediates considered are either dried biomass from forest residues, or bark, upgraded at pulp mills, or pellets from sawdust upgraded at sawmills. The findings show that the difference in performance between the studied value chains is generally small. The highest cost and significantly lowest energy efficiency are associated with the value chain with pellets, which leads to the conclusion that more pretreatment than what is required by the SNG process, to lowe r transport costs, is not profitable. Drying forest residues at pulp mills before further transportation to and upgrading at an SNG plant leads to somewhat higher transportation costs because of the relatively high fixed costs associated with transportation. However, the benefit of drying the biomass using excess heat at pulp mills is that heat is “moved” from a location, where it can be hard to find profitable ways to use it, to the SNG plant, where the excess heat can be used for district heating. With these two factors working in opposition, the total cost is similar if forest residues are transported directly to the SNG plant or via a pulp mill. The lowest cost is achieved when falling bark from pulp mills is used because the first transportation step is avoided and no additional investment for biomass handling at the mill is required. However, there is a technical uncertainty regarding how much bark can be used in the SNG process

Multi-aspect evaluation of integrated forest-based biofuel productionpathways: : Part 2. economics, GHG emissions, technology maturity andproduction potentials

Promoting the deployment of forest-based drop-in and high blend biofuels is considered strategically important in Sweden but many aspects of the overall performance of the foremost production technologies are as yet unexamined. This paper evaluates the technology maturity, profitability, investment requirements, GHG performance and Swedish biofuel production potential of six commercially interesting forest-based biofuel production pathways. Significant heterogeneity in technology maturity was observed. Lack of technical demonstration in industrially representative scales renders the liquefaction-hydrotreatment route for drop-in biofuels less mature than its gasification-catalytic upgrading counterpart. It is a paradox that short-term priority being accorded to pathways with the lowest technology maturity. Nth-of-a-kind investments in (a) gasification-based methanol, (b) hydropyrolysis-based petrol/diesel, and (c) lignin depolymerization-based petrol/diesel were profitable for a range of plant sizes. The profitability of pulp mill-integrated small gasification units (<100 MW) goes against the common perception of gasification being economically feasible only in large scales. New low-cost options for debottlenecking production at recovery boiler-limited kraft mills appear worth investigating. GHG emission reductions ranged from 66 to 95%; a penalty was incurred for high consumption of natural gas-based hydrogen. Swedish biofuel production potentials ranged from 4 to 27 TWh/y but a more feasible upper limit is 12–15 TWh/y

Value chains for production of Renewable Transportation Fuels Using Intermediates

An increased share of renewable transportation fuels requires utilisation of new low-cost sources of bio-based raw materials other than what is currently used in the pulp and paper industry and for power and district heat generation in the bioenergy sector. Currently, proposed raw material includes forest residues (branches and tops), stumps, waste round wood and different by-products from pulp and pa-per industry and sawmills. Of these, forest residues and stumps have, by far, the largest potential for increased utilisation. However, these types of raw materials are often voluminous and heterogeneous and are difficult to handle in existing refineries for production of transportation fuels. The cost of transporting this type of raw material over large distances in order to supply a larger plant is often said to be high. This report includes an analysis of the possible advantages and disadvantages of transform-ing forest-based biomass to an intermediate product with a higher energy density that is more homo-geneous and easier to handle during transport and during final conversion to transportation fuel.Two value chains are investigated as case studies a) bio-SNG production using forest residues, bark and sawdust as raw material and b) bio-oil production from forest residues, lignin in black liquor and tall oil, which can be upgraded to transportation fuels at a refinery. In the study we have assumed that the conversion of the original biomass to an intermediate product mainly takes place at a pulp mill. The intermediate conversion technologies included for value chain a) are drying and pelletizing and for value chain b) pyrolysis and distillation. The final conversion to end product bio-SNG takes place in connection to a district heating system, and the final deoxygenation and upgrading of bio-oil to hydrodeoxygenated (HDO) oil takes place at an oil refinery. The value chains with intermediates are compared with value chains without intermediates where the entire conversion process to final product is located in connection to a district heating system in value chain a) and at a stand-alone plant near to a refinery in value chain b). The value chains are studied from a well-to-gate perspective, from extrac-tion of the forest biomass to produced bio-SNG/HDO bio-oil. A direct comparison between value chains for bio-SNG and bio-oil production should be avoided. They are based on different reference data that are not synchronized. A direct comparison between the chains should in addition be done in a well-to-wheel perspective.The results show that the initial hypothesis that local production of a more energy dense intermediate would reduce transportation costs could not be verified. The reason is primarily the introduction of a second transport step to transport the intermediate to the final conversion site in addition to the transport of the raw material. The transport costs are associated with relatively high fixed cost espe-cially for ship and train transport, so the introduction of a second relatively high fixed transport cost of the intermediate has a dominating effect. Further, it can be concluded that the transport cost make up a relatively small share of the total production cost of the final product, in the order of 10%, and in a few cases up to 20%. There is therefore a relatively small difference in total specific production cost for the final product between value chains with and without intermediates considering the level of uncer-tainty in the input data and the assumptions behind the scenarios studied.Summarizing, the results indicate that the production costs are highly sensitive to the economies of scale, oxygen content in the bio-crude oil and raw material costs (forest residues price or electricity price in the case where lignin is used as raw material). Transportation costs have, comparatively, a little effect in the total production cost

Value chains for production of Renewable Transportation Fuels Using Intermediates

An increased share of renewable transportation fuels requires utilisation of new low-cost sources of bio-based raw materials other than what is currently used in the pulp and paper industry and for power and district heat generation in the bioenergy sector. Currently, proposed raw material includes forest residues (branches and tops), stumps, waste round wood and different by-products from pulp and pa-per industry and sawmills. Of these, forest residues and stumps have, by far, the largest potential for increased utilisation. However, these types of raw materials are often voluminous and heterogeneous and are difficult to handle in existing refineries for production of transportation fuels. The cost of transporting this type of raw material over large distances in order to supply a larger plant is often said to be high. This report includes an analysis of the possible advantages and disadvantages of transform-ing forest-based biomass to an intermediate product with a higher energy density that is more homo-geneous and easier to handle during transport and during final conversion to transportation fuel.Two value chains are investigated as case studies a) bio-SNG production using forest residues, bark and sawdust as raw material and b) bio-oil production from forest residues, lignin in black liquor and tall oil, which can be upgraded to transportation fuels at a refinery. In the study we have assumed that the conversion of the original biomass to an intermediate product mainly takes place at a pulp mill. The intermediate conversion technologies included for value chain a) are drying and pelletizing and for value chain b) pyrolysis and distillation. The final conversion to end product bio-SNG takes place in connection to a district heating system, and the final deoxygenation and upgrading of bio-oil to hydrodeoxygenated (HDO) oil takes place at an oil refinery. The value chains with intermediates are compared with value chains without intermediates where the entire conversion process to final product is located in connection to a district heating system in value chain a) and at a stand-alone plant near to a refinery in value chain b). The value chains are studied from a well-to-gate perspective, from extrac-tion of the forest biomass to produced bio-SNG/HDO bio-oil. A direct comparison between value chains for bio-SNG and bio-oil production should be avoided. They are based on different reference data that are not synchronized. A direct comparison between the chains should in addition be done in a well-to-wheel perspective.The results show that the initial hypothesis that local production of a more energy dense intermediate would reduce transportation costs could not be verified. The reason is primarily the introduction of a second transport step to transport the intermediate to the final conversion site in addition to the transport of the raw material. The transport costs are associated with relatively high fixed cost espe-cially for ship and train transport, so the introduction of a second relatively high fixed transport cost of the intermediate has a dominating effect. Further, it can be concluded that the transport cost make up a relatively small share of the total production cost of the final product, in the order of 10%, and in a few cases up to 20%. There is therefore a relatively small difference in total specific production cost for the final product between value chains with and without intermediates considering the level of uncer-tainty in the input data and the assumptions behind the scenarios studied.Summarizing, the results indicate that the production costs are highly sensitive to the economies of scale, oxygen content in the bio-crude oil and raw material costs (forest residues price or electricity price in the case where lignin is used as raw material). Transportation costs have, comparatively, a little effect in the total production cost

Evaluation of alternative routes for production of bio-oil from forest residues and kraft lignin

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