Total Site Analysis (TSA) Stenungsund

Rapport, 2010

This project was carried out in cooperation between the Division of Heat and Power Technology at Chalmers University of Technology, CIT Industriell Energianalys AB, AGA Gas AB, Akzo Nobel Sverige AB, Borealis AB, INEOS Sverige AB and Perstorp Oxo AB. A Total Site Analysis (TSA) was performed in this study which can be used as a basis for future implementations of energy system integration at the chemical cluster in Stenungsund. At first stream data (Tstart, Ttarget, Q) and data on overall utility consumption of all the processes in the cluster was collected. The analysis is based on data collected on process streams heated or cooled with utility exceeding a heat load of 300 kW. Additionally steam from by-product incineration which cannot be utilised in another way is considered as process heat. With this data the current energy system was analysed by determining steam excess and deficit at each steam level and company. After that, the data was represented in curves, the so called total site profiles (TSP) and the total site composite curves (TSC). The curves were used to determine the site pinch (the limiting factor for further integration) and to identify measures to increase heat recovery. The measures found by TSA were assessed qualitatively with respect to feasibility to determine the most attractive measures. Finally the site wide potential for cogeneration and measures for reduction of external cooling demand below ambient temperature was analysed. Main findings are presented in the following: From the stream data collected is can be seen that the total demand of hot and cold utility of the cluster is 442 MW and 953 MW respectively. By-products, which have to be incinerated on-site provide 40 MW of steam. To cover the external heat demand additional 122 MW of heat is supplied by steam/hot oil from boilers or directly by flue gas from added fuels purchased or available on site. The TSP and TSC curves show a site pinch at the 2 bar(g) steam system (132 °C). The site pinch limits the potential for heat integration. To increase energy savings by heat integration it is necessary to change the position of the site pinch. It was shown that theoretically by introducing a site-wide hot water circuit, increased recovery of 2 bar(g) steam and adjustment steam levels in several heat exchangers the pinch point can be moved so that hot utility savings of 122 MW plus excess of 7 MW steam at 85 bar(g) can be realised. Only introducing a hot water circuit can save 51 MW of steam from added fuels, which corresponds to estimated savings of 122 MSEK/year. It is possible to replace more steam by hot water, but the demand for 2 bar(g) steam is limited. Therefore a demand for low pressure steam must be created by adjusting steam levels in order to utilise more waste heat in a hot water circuit. The present delivery of heat to the district heating system is not affected by a site wide hot water circuit. There is potential for increased recovery of 33 MW of 2 bar(g) steam from process heat. This would replace the production of the same amount of steam in the boilers, worth 79 MSEK/year. A qualitative assessment on the implementation of a hot water circuit shows estimated steam savings of 55.2 MW (132 MSEK/year) with moderate changes (83.5 MW including more complex changes, 200 MSEK/year). Technically the introduction of a hot water circuit includes hot water pipes between several plants, as most of the consumers of heat are situated at the cracker site and at Perstorp but the sources are spread out across the cluster. Also piping is necessary to transfer the 2 bar(g) steam replaced by hot water to other plants with steam deficit. The practical potential for increased 2 bar(g) steam recovery is estimated to 4.2 MW (10 MSEK/year) with moderate changes and 26.6 MW including more complex changes (64 MSEK/year). Increased 2 bar(g) recovery implies the construction of steam pipes from Borealis to Perstorp and INEOS, as most of the potential steam sources are located at Borealis but Perstorp and INEOS have a demand for 2 bar(g) steam The theoretical cogeneration potential in the cluster is 19 MWel in addition to the 10 MWel generated today (additional revenue is 40 MSEK/year) assuming that steam demand at all pressure levels remains the same but the steam systems are connected with each other. A practical option to increase cogeneration with the existing equipment is to supply steam below 8.8 bar(g) produced at Borealis to INEOS, Akzo and Perstorp. This would result in additional 8.6 MWel by cogeneration in Borealis turbo-alternator (estimated revenue: 18 MSEK/year). Some process streams below ambient temperature are heated with steam. It has been shown that 6.5 MW steam is used for heating stream well below ambient temperature. This steam can be saved and the cooling energy can be recovered. This decreases the energy usage in the cooling system and also saves heating steam. Savings up to 48 MSEK/year were estimated. It has been shown that by site wide collaboration it is possible to increase heat recovery, cogeneration and utilisation of waste heat. The results from this study are the bases to identify concrete projects which contribute to cost and CO2 emissions savings. The study also shows the advantages of TSA in order to find solutions for process integration by the utility system on a site wide level.