Utvärdering av vattenrening och identifiering avförluster m a p energi vid Bravikens pappersmaskin 53
This Master degree project has been performed at the Braviken paper mill on papermachine 53 (PM53) which produces newsprint paper. The current economic situationhas contributed to declining demand for newsprint, which means it is extra important tobe competitive by high energy efficiency. Particularly as energy prices are expected torise when the economic growth returns.One way to increase energy efficiency is by reducing the water use in paper and pulpmills and consequently save energy through reduced heating of water. The thesis's maintask is to evaluate whether a water purification plant (microflotation plant) forpurification of process water in PM 53 is profitable. The microflotation plant enablesreuse of warm process water instead of losing the energy to receiving waters. The thesisalso aims at identifying other positions where losses occur.The water and energy flows within and around PM 53 are complex. A systemdescription and a flowchart have been established to create an overall picture of theflows. Further, a water balance of all the flows passing to and from PM 53 has beencreated. Also, based on the water balance and the temperatures of the flows, an energybalance has been established.The profitability of investing in a microflotation plant was evaluated using theknowledge gained while working with the system description, flowchart, water andenergy balance. The evaluation of the microflotation plant showed that it is not possibleto achieve good enough profitability in such an investment. The reason is that theinvestment cost is high while the reduction of steam consumption used for heating is toosmall.The evaluations of the microflotation plant lead to a deeper knowledge about thesystems used for heating of water. The deeper knowledge resulted in proposals withgreat savings potential, but with low investment costs. Those are:Eliminate a cooling water flow to the hot water tankUse water in two positions without additional heatingOptimize the heat recovery towers by increasing the dew point One of the other losses that were identified was a cooling water flow which is 48oC andtoday released into sewers. The cooling power of this cooling water flow is 720 kW andshould be used for heating.In addition to the measures mentioned in this report, there is great potential to reduceenergy use in the PM 53. To achieve this, lot of work is required. To begin with anaudit, of which temperatures and volume flows are required in all energy usingpositions in the PM 53, could be done. Furthermore, should all the energy losses (lowtemperature flows) leaving the PM 53 be identified. When the audit and identificationwork is performed the results can be used to match the revised requirements in variouspositions with the available low temperature flows.