Techno-Economic Studies of Coal-Biomass to Liquids (CBTL) Plants with CO2 Capture and Storage (CCS)

Due to insecurity in the crude oil supply and global warming, various alternative technologies for fuel production are being investigated. In this project, indirect, direct, and hybrid liquefaction routes are investigated for production of transportation fuels from coal and biomass. Indirect coal liquefaction (ICL) and direct coal liquefaction (DCL) technologies are commercially available, but both processes are plagued with high carbon footprint. Furthermore, significant amount of hydrogen is required in the DCL process leading not only to higher cost but resulting in considerable amount of CO2 production. Addition of biomass and application of carbon capture and storage (CCS) technologies are studied for reducing the carbon footprint. However, these two options can lead to higher capital and operating costs. Due to easy availability and low cost of the shale gas in the U.S., utilization of shale gas in the direct and hybrid routes was investigated for producing hydrogen at a lower cost with reduced CO2 emission in comparison to the traditional coal gasification route. Because the quality of the syncrude produced from ICL and DCL technologies vary widely, the hybrid coal liquefaction technology, a synergistic combination of ICL and DCL technologies, is investigated for reducing the penalty of downstream syncrude upgrading unit through optimal blending.;In the indirect CBTL plant, coal and biomass are first gasified to syngas. Then the syngas is converted to syncrude via Fischer-Tropsch (FT) synthesis. CO2 is captured from both raw syngas and FT vapor product. In the direct CBTL plant, coal and biomass are directly converted into syncrude in the catalytic two-stage liquefaction (CTSL) unit by adding hydrogen produced from gasification of coal/biomass/liquefaction residue or reforming of shale gas. Significant amount of CO2 that is generated in the hydrogen production unit(s) is captured to satisfy the target extent of CO2 capture. In the hybrid CBTL plant, pre-processed coal and biomass are sent to either syngas production unit or the CTSL unit. Produced syngas is sent either to FT unit or hydrogen production unit. Naphtha and diesel products from the FT unit and the CTSL unit are blended to reduce the syncrude upgrading penalty. Different CCS technologies are considered and optimized for the indirect, direct and hybrid CBTL plant depending on the sources of CO2 containing stream and corresponding CO2 partial pressure.;While several studies have been conducted for indirect CBTL processes, studies on direct and hybrid CBTL processes at the systems level and investigation of CCS technologies for these processes are scarce. With this motivation, high fidelity process models are developed for indirect, direct, and hybrid CBTL plants with CCS. These models are leveraged to perform comprehensive techno-economic studies. Contributions of this project are as follows: (1) development of the systems-level and equipment-level process models and rigorous economic models in Aspen Plus, Aspen Custom Modeler, Aspen Exchanger Design and Rating, and Aspen Process Economic Analyzer platforms, (2) sensitivity studies to analyze the impact of key design parameters (i.e. biomass/coal ratio, operating conditions of key equipment, extent of CCS, CCS technologies, blending ratio of the syncrude and products in the hybrid route) and investment parameters (i.e. price of coal and biomass, project life, plant contingency and plant capacity) on key efficiency measures, such as thermal and carbon efficiency, as well as economic measures, such as the net present value, internal rate of return and break-even oil price, (3) comparisons and analyses of trade-offs of indirect, direct, and hybrid CBTL technologies

Technoeconomic analysis of biorefinery based on multistep kinetics and integration of geothermal energy

In this work, a technoeconomic study is conducted to assess the feasibility of integrating geothermal energy into a biorefinery for biofuel production. The biorefinery is based on a thermochemical conversion platform that converts 2,000 metric tons of corn stover per day into biofuels via gasification. Geothermal heat is utilized in the biorefinery to generate process steam for gasification and steam-methane reforming. A process simulation model is developed to simulate the operation of the proposed biorefinery, and corresponding economic analysis tools are utilized to predict the product value. Process steam at 150 ºC with a flow rate of approximately 16 kg/s is assumed to be generated by utilizing the heat from geothermal resources producing a geothermal liquid at 180 °C and a total flowrate of 105 kg/s. In addition to the use for gasification and steam-methane reforming, additional geothermal capacity at 100 kg/sec from multiple wells is used for electricity production via Organic Rankine Cycle to add to the profitability of the biorefinery. The total capital investment, operating costs, and total product values are calculated considering an operating duration of 20 years for the plant and the data are reported based on the 2012 cost year. Simulation results show that the price of the fuel obtained from the present biorefinery utilizing geothermal energy ranges from $5.18 to$5.50 per gallon gasoline equivalent, which is comparable to $5.14 using the purchased steam. One important incentive for using geothermal energy in the present scenario is the reduction of greenhouse gas emissions resulting from the combustion of fossil fuels used to generate the purchased steam. Geothermal energy is an important renewable energy resource, and this study provides a unique way of integrating geothermal energy into a biorefinery to produce biofuels in an environmentally friendly manner. In the other part of the study, the simulation of biomass gasification is carried out using multistep kinetics under various oxygen-enriched air and steam conditions. The oxygen percentage is increased from 21% to 45% (by volume). Five different kinds of biomass feedstocks including pine wood, maple-oak mixture (50/50 by weight), seed corn, corn stover, and switchgrass are used in this study. The bed temperature is maintained at 800 oC. Different conditions such as flowrates of biomass and different oxygen-enriched air and steam ratios are used to simulate different cases. The simulation results for different species are in good agreement with the experimental data.. From the results, it is evident that the proposed gasification kinetics model can predict the syngas compositions. The model is able to capture the effects of biomass feedstock and oxygen and steam concentrations. The model is able to predict the concentrations of H2, CO, CO2, H2O, CH4, N2 in the syngas; nonetheless, more rigorous simulation has to be carried out to model NOx, NH3, and other higher alkane and alkenes such as C2H4, C2H2, C2H6 etc

Technical, Economic and Environmental Assessment of Energy Generation using Bioenergy with Carbon Capture, Utilisation and Storage.

Bioenergy with Carbon Capture and Storage is a promising negative emissions technology to mitigate climate change across different sectors. This thesis explores the application potential of this technology in energy generation by evaluating the technical, economic and environmental performance to present detailed information for the literature. This will help stakeholders including researchers, policymakers and the public make informed choices on the best route to decarbonisation. In power generation, the performance of different types of biomass, coupled with different CO2 abatement technologies, has been evaluated. The performance of each case has been thoroughly assessed against technical, economic and environmental parameters, then benchmarked against natural gas in power generation. An analysis to determine the effect on carbon pricing as an economic tool has been explored as well as a sensitivity analysis to identify the most significant factors influencing the production of electricity. In fuel generation, the production of Fischer-Tropsch fuels, synthetic natural gas and oxymethylene ethers via biomass gasification without carbon capture and storage and with carbon capture and storage has been assessed. After modelling and simulation in Aspen Plus to determine the mass and energy balances, an economic model has been developed in Microsoft Excel to estimate the capital costs, operating costs, levelised costs of energy and minimum selling prices; and the greenhouse gas emission factors have been estimated to investigate the environmental effect. Then, fuel generation via electrochemical conversion and CO2 utilisation has been considered. The electrofuel production routes have focused on storing renewable energy in fuels. The gasification step has been replaced with an electrolyser to produce H2 in addition to the CO2 captured from different sources to produce the same fuels. The environmental assessment compared different CO2 sources on the mitigation potential of each electrofuel production route. In conclusion, energy generation via bioenergy with CCS cannot currently compete with energy generation using fossil fuels mainly due to the higher levelised costs of energy but with the use of carbon pricing in the range of £48/tCO2 and £146/tCO2, such that these plants are rewarded for each tonne of CO2 removed and the fossil-fuel plants are penalised, fossil-fuel energy generation could be phased out faster to achieve decarbonisation. Also, these routes show promising mitigation potential with the ability to remove up to 1.52 Mt of CO2 per year from the atmosphere. With electrofuel production, there is more work to be done to attain feasibility and this is mainly due to the cost of electricity which is the major expense in the economics; also, CO2 storage needs to be coupled with CO2 utilisation to increase the chances of achieving negative emissions

Design of a H2 pressure swing adsorption process at an advanced IGCC plant for cogenerating hydrogen and power with CO2 capture

Strong dependency on fossil fuels and the associated price and supply chain risk increase the need for more efficient utilisation of existing non-renewable energy sources. Carbon capture and hydrogen purification technologies are expected to play a key role in the future low-carbonised energy matrix. Integrated Gasification Combined Cycles (IGCCs) are one of the emerging clean coal technologies which pave the way for producing power from coal with a higher net power efficiency than conventional PC-fired boiler power plants. It is also advantageous that in an IGCC power plant a carbon capture unit can be applied to a stream having a very high CO2 partial pressure ahead of gas combustion that would not be available in case of a PC-fired boiler power plant, leading to less energy penalty involved in carbon capture. At the same time, the production of ultrapure hydrogen is both a sought target and an appropriate environmental solution because it is commonly utilised as feedstock in refineries’ hydrotreaters and hydrocrackers as well as energy carrier in fuel cells. A high purity of hydrogen has been commercially produced out of raw synthesis gas using a Hydrogen Pressure Swing Adsorption (H2 PSA) process. In this thesis, it was aimed to design and optimise a bespoke H2 PSA system tailored for a decarbonised syngas feed originating from a carbon capture unit. Therefore, a novel H2 PSA has been studied that is applied to an advanced IGCC plant for cogenerating power and ultrapure hydrogen (99.99+ mol%) with pre-combustion CO2 capture. In designing the H2 PSA, it is essential to increase the recovery of ultrapure hydrogen product to its maximum since the power consumption for compressing the H2 PSA tail gas up to the gas turbine operating pressure should be minimised to save the total auxiliary power consumption. Hydrogen recovery was raised by increasing the complexity of the PSA step configuration that allows a PSA cycle to have a lower feed flow to one column being used for adsorption and more pressure equalisation steps. An in-depth economic analysis was carried out and discussed in detail. The industrial advanced IGCC performances have also been improved by process integration between the H2 PSA unit and other units in the plant

Studying the Role of System Aggregation in Energy Targeting: A Case Study of a Swedish Oil Refinery

The definition of appropriate energy targets for large industrial processes is a difficult task since operability, safety and plant layout aspects represent important limitations to direct process integration. The role of heat exchange limitations in the definition of appropriate energy targets for large process sites was studied in this work. A computational framework was used which allows to estimate the optimal distribution of process stream heat loads in different subsystems and to select and size a site wide utility system. A complex Swedish refinery site is used as a case study. Various system aggregations, representing different patterns of heat exchange limitations between process units and utility configurations were explored to identify trade-offs and bottlenecks for energy saving opportunities. The results show that in spite of the aforementioned limitations direct heat integration still plays a significant role for the refinery energy efficiency. For example, the targeted hot utility demand is reduced by 50-65% by allowing process-to-process heat exchange within process units even when a steam utility system is available for indirect heat recovery. Furthermore, it was found that direct process heat integration is motivated primarily at process unit level, since the heat savings that can be achieved by allowing direct heat recovery between adjacent process units (25-42%) are in the same range as those that can be obtained by combining unit process-to-process integration with site-wide indirect heat recovery via the steam system (27-42%)

ECOS 2012

The 8-volume set contains the Proceedings of the 25th ECOS 2012 International Conference, Perugia, Italy, June 26th to June 29th, 2012. ECOS is an acronym for Efficiency, Cost, Optimization and Simulation (of energy conversion systems and processes), summarizing the topics covered in ECOS: Thermodynamics, Heat and Mass Transfer, Exergy and Second Law Analysis, Process Integration and Heat Exchanger Networks, Fluid Dynamics and Power Plant Components, Fuel Cells, Simulation of Energy Conversion Systems, Renewable Energies, Thermo-Economic Analysis and Optimisation, Combustion, Chemical Reactors, Carbon Capture and Sequestration, Building/Urban/Complex Energy Systems, Water Desalination and Use of Water Resources, Energy Systems- Environmental and Sustainability Issues, System Operation/ Control/Diagnosis and Prognosis, Industrial Ecology

Process Design and Optimization of Biorefining Pathways

Synthesis and screening of technology alternatives is a key process-development activity in the process industries. Recently, this has become particularly important for the conceptual design of biorefineries. A structural representation (referred to as the chemical species/conversion operator) is introduced. It is used to track individual chemicals while allowing for the processing of multiple chemicals in processing technologies. The representation is used to embed potential configurations of interest. An optimization approach is developed to screen and determine optimum network configurations for various technology pathways using simple data. The design of separation systems is an essential component in the design of biorefineries and hydrocarbon processing facilities. This work introduces methodical techniques for the synthesis and selection of separation networks. A shortcut method is developed for the separation of intermediates and products in biorefineries. The optimal allocation of conversion technologies and recycle design is determined in conjunction with the selection of the separation systems. The work also investigates the selection of separation systems for gas-to-liquid (GTL) technologies using supercritical Fischer-Tropsch synthesis. The task of the separation network is to exploit the pressure profile of the process, the availability of the solvent as a process product, and the techno-economic advantages of recovering and recycling the solvent. Case studies are solved to illustrate the effectiveness of the various techniques developed in this work. The result shows 1, the optimal pathway based on minimum payback period for cost efficiency is pathway through alcohol fermentation and oligomerized to gasoline as 11.7 years with 1620 tonne/day of feedstock. When the capacity is increased to 120,000 BPD of gasoline production, the payback period will be reduced to 3.4 years. 2, from the proposed separation configuration, the solvent is recovered 99% from the FT products, while not affecting the heavier components recovery and light gas recovery, and 99% of waster is recycled. The SCF-FT case is competitive with the traditional FT case with similar ROI 0.2. 3, The proposed process has comparable major parts cost with typical GTL process and the capital investment per BPD is within the range of existing GTL plant

CO2 capture using monoethanolamine solutions : development and validation of a process model based on the SAFT-VR equation of state

The development of a predictive model for an absorber-desorber process for the separation of carbon dioxide (CO2) from a gas stream using an aqueous alkanolamine solution as a solvent is presented. Post-combustion carbon dioxide capture by absorption with aqueous amine solvents is likely to play an important role in climate change mitigation, by helping to reduce a significant fraction of CO2 emissions from fossil fuel power plants. There are, however, a number of concerns with the large scale deployment of this technology, including energy requirements, solvent degradation and the environmental and health impact resulting from a potential loss of solvent and solvent degradation products. Modelling studies can play an invaluable and complementary role in addressing some of these issues, including the choice of solvent and operating conditions that yield optimal performance. The model presented here incorporates state-of-the-art SAFT-VR thermodynamics into a rate-based process model. A characteristic of the proposed approach is that all the reactions are treated within a thermodynamic description, assuming chemical equilibrium throughout. This greatly reduces the amount of experimental data required to model the behaviour of the absorber. Furthermore, in contrast with many treatments of reactive systems of this type, no enhancement factor is used in the process model. The absorber-desorber process model is implemented in the gPROMS software platform and validated using published pilot plant experimental data for the removal of CO2 from an air and CO2 stream using monoethanolamine (MEA) solutions. A scaling of the diffusivity in the liquid phase, that is found to be transferable to different operating conditions, is proposed. Reliable predictions are obtained for the temperature and composition profiles in the gas and liquid phases, including a good description of the temperature bulge which sometimes appears along the height of the absorber column. The same transferable model is used to describe both the absorber and the desorber columns. The influence of key parameters of the model for different operating conditions is assessed through a sensitivity analysis. The model developed in this study is applied to simulate a complete amine-based carbon capture absorber-desorber process. Given the relatively simple modelling of the solvent/CO2 interactions, in which the reactions are treated implicitly through a physical approach, the proposed model lends itself well to the investigation of other solvents.Open Acces