Upgrading technologies for biogas production plants. Overview and life cycle cost analysis of available technologies

Abstract

An increased focus on waste management has emerged during the last decade. Renewable energy, efficient energy usage and cuts in greenhouse gas emissions are highly prioritized by the EU. The International Energy Agency (IEA) and the World Energy Council estimates that the global energy demand will grow within the next decades. The continuously increasing energy demand, contributes to development of new technologies for utilization of alternative energy resources. Energy resources with low environmental impact should be utilized to achieve a sustainable development.

Biogas production from organic waste has shown to be more environmentally friendly compared to other waste handling options such as composting, incineration and landfilling. Biogas production from organic waste is a treatment technology that generates renewable energy in forms of biogas, and recycles organic waste as a fertilizer and soil amendment. The results of several studies show that the best climate benefit is achieved when biogas is upgraded to biomethane and substituted with diesel.

Upgrading of biogas to biomethane is performed in the upgrading system, which is an optional process in a biogas production plant. Chemical scrubber, water scrubber, organic physical scrubber, membrane, pressure swing adsorption and cryogenic upgrading are different types of commercially used biogas upgrading technologies. The total life cycle cost for an upgrading plant is affected by different factors. This includes the investment cost and the operation and maintenance cost. There are three major consumables included in the operating cost; power, water and chemicals.

In this thesis, ten different small-scale upgrading plants based on five different upgrading technologies are investigated. A life cycle cost analysis (LCCA) is conducted for all the different upgrading technologies in order to find the most cost-effective system. Two different scenarios are analyzed; one where excess heat from the upgrading units is utilized, and one without heat recovery of the excess heat. By including heat recovery in the LCCA, it is possible to compare different upgrading technologies with respect to the whole biogas production plant.

The data used in the analysis are collected from various manufacturers for biogas upgrading plants. All the costs associated with the investment, operation and maintenance are identified and used in the LCCA. The collected data was given either as a fixed average number, or as a range with a minimum and maximum value. To account for the uncertainties in the data, an uncertainty analysis was conducted using a Monte Carlo simulation technique. For this aim, statistical approaches were used by developing different codes in Matlab to perform the uncertainty analysis. Furthermore, a sensitivity analysis is done in order to test the outcome of the LCCA by changing the electricity cost and discount rate in the initial analysis.

Results from this thesis is applicable for companies considering investing in a biogas upgrading plant. Information regarding the cost and consumables for different technologies are presented. Electricity price and access to water and chemicals, may affect the decision-making for selection of biogas upgrading technology. The LCCA shows that pressure swing absorption and water scrubber are the most cost-effective upgrading technologies for both with and without heat recovery. The least cost-effective technologies was found to be the cryogenic upgrading and amine scrubber.