Thermal Process Integration Research Articles

Waste-to-energy innovative system: Assessment of integrating anaerobic digestion and pyrolysis technologies

Anaerobic digestion (AD) of sewage sludge is an already well-developed technology to convert waste to bioenergy and digestate. Despite its deployment, AD process still raises environmental, technical and economic issues and many researches have been done to improve the process yield, reduce environmental burdens from digestate application and allow a better distribution of energy. The integration of thermal processes with anaerobic digestion is explored to overcome some of the anaerobic digestion limitations. In this study, a cradle-to-grave life cycle assessment (LCA) is performed to compare a system integrating anaerobic digestion and pyrolysis (PY) with single anaerobic digestion, for the co-digestion of sewage sludge and quinoa residue. The results suggest that the environmental impacts of the two pathways are quite similar except for three impact categories: single anaerobic digestion is the best scenario in terms of global warming potential (−769 vs. -604 kg CO 2 eq./t substrate), ozone depletion (−33.7 vs −2.11 mg CFC-11 eq./t substrate) and fossil resources use (−9900 vs −6900 MJ/t substrate). The multifunctional process could be a viable competitor to single anaerobic digestion by improving pyrolysis products upgrading. The application of liquid digestate to crop field revealed to have significant burdens to particulate matter, acidification and terrestrial eutrophication impact categories and must be carefully monitored in both pathways.

Hydrothermal liquefaction of organic resources in biotechnology: how does it work and what can be achieved?

Increasing the overall carbon and energy efficiency by integration of thermal processes with biological ones has gained considerable attention lately, especially within biorefining. A technology that is capable of processing wet feedstock with good energy efficiency is advantageous. Such a technology, exploiting the special properties of hot compressed water is called hydrothermal liquefaction. The reaction traditionally considered to take place at moderate temperatures (200-350°C) and high pressures (10-25MPa) although recent findings show the benefits of increased pressure at higher temperature regions. Hydrothermal liquefaction is quite robust, and in theory, all wet feedstock, including residues and waste streams, can be processed. The main product is a so-called bio-crude or bio-oil, which is then further upgraded to fuels or chemicals. Hydrothermal liquefaction is currently at pilot/demo stage with several lab reactors and a few pilots already available as well as there are a few demonstration plants under construction. The applied conditions are quite severe for the processing equipment and materials, and several challenges remain before the technology is commercial. In this review, a description is given about the influence of the feedstock, relevant for integration with biological processing, as well as the processing conditions on the hydrothermal process and products composition. In addition, the relevant upgrading methods are presented.

Valorization of sugarcane biorefinery residues using supercritical water gasification: A case study and perspectives

The present study evaluates the use of supercritical fluid technology, particularly supercritical water gasification (SCWG), to add value to residues from a sugarcane biorefinery that produces first and second generation ethanol. This case study aims at elucidating how process system engineering tools such as thermal process integration, life cycle analysis, economic evaluation and multi-objective optimization can contribute to minimizing some future challenges of the industrial implementation of supercritical fluid-based technologies, which were discussed in the Workshop on Supercritical Fluids and Energy – SFE’13. In addition, this case study exposes future perspectives in terms of the requirements to further develop this field. The optimized solutions of the evaluated case showed that the SCWG process increases the overall efficiency of the process in terms of energy and carbon fixation. It decreases the CO2 equivalent emissions and it leads to a thermally self-sufficient process. The economic analysis showed a high investment cost but a feasibility of using the current market prices for the produced fuels and electricity.

Heat integration including heat exchangers, combined heat and power, heat pumps, separation processes and process control

This Special issue (SI) of Applied Thermal Engineering presents twenty one selected contributions from the 14th Conference Process Integration, Modelling and Optimisation for Energy Saving and Pollution Reduction– PRES’11. It benefits from the long-term cooperation between the PRES conferences and the journal. The selected papers cover important subjects: heat exchangers and heat pumps, design of thermal processes, heat integration, combined heat and power (CHP) integration, integration of thermal processes, power systems.

Thermal process integration in the AVDU A12/2 crude distillation unit during winter operation

A pinch analysis of the AVDU A12/2 crude distillation unit processing 2 million tons of crude oil per year is made. A pinch retrofit of the recuperative heat-exchange system of the unit is performed. It is shown that the implementation of the proposed project will reduce the arbitrary energy consumption by 60%, which corresponds to a reduction in specific fuel consumption from 36 to 13 kg per ton of refined oil.

Future CO 2 removal from pulp mills – Process integration consequences

Earlier work has shown that capturing the CO 2 from flue gases in the recovery boiler at a pulp mill can be a cost-effective way of reducing mill CO 2 emissions. However, the CO 2 capture cost is very dependent on the fuel price. In this paper, the potential for reducing the need for external fuel and thereby the possibility to reduce the cost for capturing the CO 2 are investigated. The reduction is achieved by using thermal process integration. In alternative 1, the mill processes are integrated and a steam surplus made available for CO 2 capture, but still there is a need for external fuel. In alternative 2, the integration is taken one step further, the reboiler is fed with MP steam, and the heat of absorption from the absorption unit is used for generation of LP steam needed at the mill. The avoidance costs are in both cases lower than before the process integration. The avoidance cost in alternative 1 varies between 25.4 and 30.7 EUR/tonne CO 2 depending on the energy market parameters. For alternative 2, the cost varies between 22.5 and 27.2 EUR/tonne CO 2. With tough CO 2 reduction targets and correspondingly high CO 2 emission costs, the annual earnings can be substantial, 18.6 MEUR with alternative 1 and 21.2 MEUR with alternative 2.

Pinch analysis of a model mill: Economic and environmental gains from thermal processintegration in a state-of-the-art magazine paper mill

A model of a modern magazine paper mill has been investigated from an energy perspective. The mill’s refining process has a power demand of 100 MW (3050 kWh/ADt pulp), and 86 MW of this is recovered as steam. Since the steam demand of the mill is low, there is a steam surplus of 21.5 MW. The steam surplus could be increased by 41 % through thermal process-integration. Simultaneously the cooling demand decreased by 13.2 MW or 49 %, resulting in reduced cooling costs and decreased thermal pollution. The financial evaluation, for which a grass-root situation was assumed, shows promising economy if the mill can sell the surplus heat (e.g. to a district heating system): the marginal payback period for increasing the steam surplus would be less than a year, even with low energy prices. If the surplus steam has to be used on site, power generation in a condensing steam turbine is an option. The financials for increasing the power generation are very dependent on the power price, but with current Swedish power prices the marginal payback period would be 3 to 4 years. Energy exports, whether heat or power, would presumably replace fossil fuel. Consequently, the greenhouse gas emissions in society would decrease by thousands of tons per year. In the future it might be possible to decrease the power consumption in the refining process, resulting in a decrease of the steam surplus. With process integration, the power input can be decreased by 30 % before there is a steam deficit. This option offers a good opportunity for profit as well as decreased environmental impact.