Bilal Patel

Producing Transportation Fuels with Less Work

New reaction chemistry may reduce the energy input and carbon dioxide emissions from processes that convert coal into liquid fuels.

A Thermodynamic Targeting Approach for the Synthesis of Sustainable Biorefineries

Abstract One of the major challenges of achieving a sustainable integrated biorefinery lies in the systematic synthesis and design of such systems. There is a need to develop quick and efficient methods to screen the various product options in order to determine which products best utilise the feedstock. This contribution develops upfront conceptual-level design targets for the production of fuels and chemicals from biomass. These targets aim to provide insight into the design of sustainable biorefineries, prior to the detailed design, with an aim of maximising feedstock utilisation thereby increasing the process efficiency and reducing the emissions from such processes. The targets for these different products are compared using sustainability metrics such as Atom Economy and E-factor. Products which maximise the Atom Economy are determined. This work further identifies integration opportunities and assesses whether combining the production of fuels and chemicals can achieve higher process efficiencies.

Making processes work

Abstract Chemical processes and their flow-sheets are systems and as with all systems one cannot optimise each part alone and expect to get an optimal process. One also has to take into account the connections and interactions between the parts of the systems in order to achieve the global optimum. In this paper fundamental thermodynamics will be used to show how to achieve an optimal solution. A coal-to-liquids (CTL) process will be used to illustrate the method. The overall material balance for a process will be looked at first. This material balance must include the constraints such as the energy (heat and work) balance and thus must include the feed streams that supply utilities, such as heat and electricity to the process. The best material balance ensures that as much of the feed material ends up in the product. In the examples discussed, focus will be on ensuring that as much of the carbon in the feed as possible ends up in the hydrocarbon product; the carbon from the feed that does not report to the product is emitted from the process as CO 2 which is undesirable for a number of reasons. The resulting overall material balance is then regarded as the process target, since it is the “best” material balance. Furthermore, the manner in which energy (heat and work) is added or removed from a process, affects the material balance by introducing irreversibilities. The greater these irreversibilities are, the further the process operates from the process target, implying that the process produces more CO 2 per mole of product produced. Many processes, such as CTL, require substantial quantities of work to be added. It is shown that this may be done by designing the overall process such that the process itself is effectively a heat engine. Thus heat at high temperature is added in an endothermic, high temperature sub-process (e.g. gasification) and (less) heat is rejected at a lower temperature from an exothermic, low temperature sub-process (e.g. Fischer–Tropsch synthesis). Just as in a heat engine, there is a relationship between the values of the high and low temperatures, the quantities of heat flowing in and out of the sub processes and the amount of work added to the overall process. One can note that any stream has an enthalpy and a temperature and these two together can be used to describe the work content of this stream. The Carnot temperature for each sub-process is defined as the temperature at which the heat added to the sub-process takes with it the work content required by the sub-process. The bigger the difference between the actual operating temperature and the Carnot temperature, the more irreversible the process is and the further away the process operates from the process target. A CTL process has been chosen to apply the methods in order to obtain the process target and the overall material balances for different options. It is shown that there are different ways of arranging the heat engine for CTL, for example indirect or direct liquefaction, and that the direct route has higher carbon efficiency than the indirect route. However it is shown that one can use the ideas in the paper to synthesise a new route for CTL where rather than gasifying to syngas, one gasifies to hydrogen and carbon dioxide followed by the FT synthesis reaction. In this way one can show that this indirect CTL route is nearly as efficient as the direct route.

Process Flow-Sheet Synthesis: Systems-Level Design applied to Synthetic Crude Production

This paper showcases a novel approach for designing concepts for process flow-sheets at the “systems-level”. A graphical technique, called the “GH-space”, is used to analyze the flows of heat and work within a process to provide insight into the interactions of various process units within the process. Any unit process, which interacts with the surroundings by transferring heat and work, can be represented as a vector on the GH-space. By manipulating these vectors, a process can be designed to meet certain design criteria or constraints. While material and energy balances are normally performed on a flowsheet, this vectored approach allows the material and energy balances to be used to construct a flowsheet. This paper focuses on the design of a flow-sheet for the production of synthetic crude oil by way of Fischer-Tropsch hydrocarbons. It was shown that a process could be designed that not only produced the desired product but could also be thermodynamically reversible and carbon neutral. The goal of this work is not to present a final optimized design but rather to call attention to the possibilities that could lead to potential solutions to the most challenging problems facing the newest generation of design engineers. Perhaps the greatest strength of the GH-space technique is that it tends towards the “best” thermodynamic solution. It may not be possible to achieve this best solution, in a practical sense, but it is invaluable in providing a basis for comparison.

Synthesis of a Biomass-to-Liquids (BTL) Process using a Hybrid Pyrolysis-Gasification System

Abstract Biomass is a promising feedstock for the production of energy and products (fuels, chemicals and materials). Thermochemical conversion technologies such as pyrolysis and gasification are attractive conversion techniques to transform biomass into a variety of products. Systematic techniques are required to synthesise and evaluate biomass conversion processes. In this work, the synthesis of Biomass-to-Liquids (BTL) systems are considered. By utilising atomic species balances and the first law of thermodynamics, various overall process configurations are developed and evaluated in terms of carbon efficiency and atom economy. Gasification, Pyrolysis and Fischer-Tropsch (FT) synthesis is utilised to attain the overall process configurations. The level of mass and energy integration required is determined. The carbon efficiency and raw material requirements for both the integrated and unintegrated processes are determined.

Analysis of the Carbon Efficiency of a Hybrid XTL-CSP process

Abstract The carbon efficiency of XTL (X- Coal, Natural gas, Biomass etc.) processes depends on the feedstock composition, especially the H content in the feedstock, and the energy requirements of the process. Low H: C ratios and high energy requirements requires extra feedstock to balance the material flows or to provide energy by combustion. This lowers the carbon efficiency, and increase the CO 2 emission of the process. The target carbon efficiency of XTL process is normally determined by the gasification process, which is highly endothermic. By employing Concentrated Solar Power (CSP) to supply the energy required for the gasification process the target carbon efficiency can be significantly improved. In the case of CTL, the carbon efficiency can be improved from around 50% to 66%, and for BTL, the carbon efficiency can be improved from around 60% to 70%. Furthermore, by changing the overall mass balance of XTL processes that employ CSP, a carbon efficiency of 100% can be achieved. One such possible process mass balance is: C H x O y + 1 − x / 2 H 2 O → C H 2 + 1 + y − x / 2 / 2 O 2