Black Liquor Gasification
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WHAT IS THE CHALLENGE?Spent liquors (black liquor) from pulping contribute with about 40 TWh/annum to the Swedish energy balance. The current technology for energy and chemical recovery is based on the so called Tomlinson boiler (recovery boiler) which combusts the biological matter in the black liquor and recycles the cooking chemicals to the pulp cycle in a suitable form. The drawback with the recovery boiler is that the overall efficiency is relatively low and that only a fraction of the thermal energy is converted to electrical power (app. 3 TWh/annum). Pulp and paper mills also need process steam which today is produced in the recovery boiler (app. 30 TWh/annum). An alternative is black liquor gasification at elevated pressure and hig temperature. This technology has a much higher overall efficiency and a potential to produce 60-70% more power than with modern recovery boilers. If all pulp mills in Sweden were converted to black liquor gasification, the increase in power production would be about 7 TWh/annum or a total production of about 10 TWh/annum. Predicted development of turbine technology towards higher temperatures would yield additional power so that the potential for power production from black liquor would be about 15 TWh/annum. A corresponding predicted development of advanced recovery boilers would yield app. 8 TWh/annum. Black liquor gasification can as an alternative to power production be used for production of transportation fuels with existing technology. The potential for this alternative is to contribute with about 30% of Sweden's total need for transportation fuels. Regardless of which of the two alternatives is chosen, a large scale change would be a major step towards sustainability since black liquor is a renewable fuel (wood from the forest). The major reason that has prevented the pulping industry to make the transition to black liquor gasification has until now been that the long term reliability and robustness of the process has been unknown. Of special interest to the pulping industry is the interaction between the gasification process and the complex pulping process. Examples of issues are whether there is a risk for enrichment of so called non-process elements or if there is a need for redesign or modification of other process equipment to accomodate the gasification process.HOW CAN THE PROGRAMME CONTRIBUTE TO A SOLUTION?
A complete gasifier unit is under construction and will undergo long term testing in an associated project. A successful outcome of this project will satisfy the pulping industry's need for proof of robustness and long term reliability. However, there are many other questions about the scalability of the process, about chemical kinetics and around process integration with the pulping process. The program addresses these issues and has the main goals to optimise the process, to find the best material choices and to show how gasification can be integrated in an optimum way with pulping.
WHO WILL BENEFIT FROM THE RESULTS?
Pulp industry - improved utilisation of raw materials and increased profit. Equipment manufacturers - sale of licenses and complete plants. Utility companies - contracts with pulping industries for green power and/or transportation fuel production from black liquor. Consumers - green fuels and green electricity at an attractive price. Society as a whole - reduced dependency on foreign resources and better environment.
