Opportunities for Process Integrated Biorefinery Concepts in the Chemical Cluster in Stenungsund
The energy and material needs of human society are increasing while at the same time fossil resources decline. Greenhouse gas (GHG) emissions are influencing the world’s climate. The potential for substituting fossil hydrocarbons in synthetic products and liquid fuels by renewable raw materials is being discussed in order to fight climate change and decrease dependency on fossil resources. The biorefinery concept is a way to accomplish this transition. A wide range of renewable raw materials can be converted into value added products and therefore substitute fossil feedstocks.
High efficiency is very important in order to profitably implement biorefinery concepts. The interest for energy combines and eco-industrial parks is increasing nowadays as they offer the opportunity to exchange materials and energy between two or more industries and also the society. Therefore integration of biorefinery concepts into industrial cluster can be advantageous.
In this study suitable biorefinery concepts are identified and analysed with respect to integration opportunities in Sweden’s largest chemical cluster in Stenungsund. Technical, economical and environmental consequences of integrating a biorefinery in the cluster compared to stand-alone operation are identified based on mass and energy balances, knowledge on the current energy situation in the cluster and the thermal characteristics of the different biorefineries.
Suitable biorefinery concepts for integration in the cluster include biomass gasification for syngas production, lignocellulosic ethanol production for conversion into ethylene and low temperature biomass drying for fuel upgrading. The current demand of steam produced in the cluster’s boilers is 122 MW at pressure levels between 85 and 1 bar(g). Excess steam from a gasification unit with an assumed operation time of 8000 h/yr can be used for cogeneration to cover parts of this demand. By integration of a gasification unit producing 160 kt_product gas/yr, 16 GWhel/yr and 128 GWhsteam/yr can be delivered to the cluster. For a stand-alone unit it is assumed that all excess steam is used for electricity production in a condensing turbine, producing 47.4 GWhel/yr. This results in increased incomes between 18.3 and 47.4 MSEK/yr in the integrated case. CO2 emissions reduction is 24.4 kt_CO2/yr higher with integration.
Ethanol production from lignocellulosic raw material yields substantial amounts of residual products which can be used for heat and power generation to cover parts of the clusters current energy demand and/or deliver heat and electricity to a downstream ethanol-to-ethylene dehydration plant. The results are obtained for a process that produces 100 kt ethylene/yr and has an operating time of 8000 h/yr. A lignocellulosic ethanol plant producing the feedstock (174 kt ethanol/yr) to an ethanol-to-ethylene plant has an energy surplus of 195.2 GWh/yr when all residues are combusted. In an integrated plant this yields 21.8 GWhel/yr and 168 GWhsteam/yr to the cluster and/or the ethanol-to-ethylene plant, while in stand-alone operation (only production of electricity from excess steam) 64.3 GWhel/yr can be produced. Incomes by integration are between 24.8 and 64.2 MSEK/yr higher and CO2 emissions reduction is increased by 31.2 kt/yr by integration.
An improved utility system for maximum energy recovery was developed in a previous total site analysis (TSA) study. The residual waste heat is 498 MW at 99 °C to 27 °C. Utilising this heat for low temperature drying of biomass was compared to stand-alone dryer operation. This gave a total potential of 4.3*106 tonnes dried biomass per year (15 wt-% moisture content). By integration 129 SEK/t_dry mass less fuel costs and 234 kg/t_dry mass less CO2 emissions where found.
Total Site Analysis.
Bio-ethanol to ethylene