Epsilon Archive for Student Projects

Abstract

Each year, the coffee machines at Ericsson in Kista produce around 100 tons of ground coffee waste.
The companies Coor Service Management, Löfbergs Lila and Selecta are all responsible for different stages in the logistical chain in delivering coffee and, together with Ericsson, they want to increase their environmental benefit. The plan is to produce biogas through anaerobic digestion instead of incinerating the coffee waste in a heating plant. The results are to be presented as different business cases in which different biogas plants are compared with the reference case (heating plant),
comparing costs and environmental impacts.

There are two major environmental benefits from producing biogas; reduced carbon dioxide emissions from when fossile fule is replaced by carbon neutral biogas, and reduced emissions from returning digestate from the bio reactor to farmland instead of using industrial fertelizer.

In order to determine the biogas potential in coffee waste, a couple of properties had to be determined in a laboratory. Properties such as the dry substance content, heating value, moisture content and ash content. The results show that 100 tons coffee waste could produce around 16 500 Nm3 biogas which would contain 163 MWh.

The biogas reactor and upgrade plant both need energy gas to function and uses around 14 MWh of the produced gas. In the end, the resulting upgraded biogas contains 149 MWh energy. Such an amount of gas can replace 15,1 m3 of diesel and thus reduce carbon dioxide emissions by 39,4 ton.
The emissions from running the reactor and upgrade plant, combined with methane leakage amounts to 4,8 ton carbon dioxide.

All of the biogas plants that were examined returns digestate and nutrients to farmlands which reduces the need for industrial fertelizer. The production of fertelizer uses alot of energy, and by returning digestate a reduction of 58 GJ energy and 3 ton CO2 can be achieved. This is not the case with the heat plant which instead has to place some of its produced ashes in landfills.

If the exergy content in the biogas is compared to that of the heat it shows that there is a point to making gas instead of incinerating the waste. The biogas has about 50 % higher exergy content than the heat has and therefore it is possible to utilize the substrate more efficiently.

Transporting coffee waste from Ericsson to different biogas plants will result in increased carbon dioxide emissions. The three plants investigated in this thesis are Henriksdals sewage treatment plant, the Himmerfjärd plant and Uppsala biogas plant. For each plant, drivning distance, pre treatment requirements of the coffee waste, and related costs were determined. Using methods from the Network for transportation and enviroment, the emissions for each case were calculated.

The results show that the Henriksdal case will increase carbon dioxide emissions by two tons per year, and the other cases will increase emissions by four tons.

The result from combining laboratory work, simulations and calculations show that the case where Henriksdal recives the coffee waste will reduce carbon dioxide emissions by 15,1 ton at a cost of 72 000 kr per year. The case with the Himmerfjärd plant will reduce emissions by 13,8 ton at a cost of 74 000 kr per year. The final case with Uppsala biogas plant will reduce emissions by 13,7 ton at the
cost of 107 000 kr per year. And thus there are environmental benefits from producing biogas from the coffee waste, but they do come at a cost.