Marie Münster

Long-term affected energy production of waste to energy technologies identified by use of energy system analysis

Affected energy production is often decisive for the outcome of consequential life-cycle assessments when comparing the potential environmental impact of products or services. Affected energy production is however difficult to determine. In this article the future long-term affected energy production is identified by use of energy system analysis. The focus is on different uses of waste for energy production. The Waste-to-Energy technologies analysed include co-combustion of coal and waste, anaerobic digestion and thermal gasification. The analysis is based on optimization of both investments and production of electricity, district heating and bio-fuel in a future possible energy system in 2025 in the countries of the Northern European electricity market (Denmark, Norway, Sweden, Finland and Germany). Scenarios with different CO(2) quota costs are analysed. It is demonstrated that the waste incineration continues to treat the largest amount of waste. Investments in new waste incineration capacity may, however, be superseded by investments in new Waste-to-Energy technologies, particularly those utilising sorted fractions such as organic waste and refuse derived fuel. The changed use of waste proves to always affect a combination of technologies. What is affected varies among the different Waste-to-Energy technologies and is furthermore dependent on the CO(2) quota costs and on the geographical scope. The necessity for investments in flexibility measures varies with the different technologies such as storage of heat and waste as well as expansion of district heating networks. Finally, inflexible technologies such as nuclear power plants are shown to be affected.

Economic and environmental optimization of waste treatment.

This article presents the new systems engineering optimization model, OptiWaste, which incorporates a life cycle assessment (LCA) methodology and captures important characteristics of waste management systems. As part of the optimization, the model identifies the most attractive waste management options. The model renders it possible to apply different optimization objectives such as minimizing costs or greenhouse gas emissions or to prioritize several objectives given different weights. A simple illustrative case is analysed, covering alternative treatments of one tonne of residual household waste: incineration of the full amount or sorting out organic waste for biogas production for either combined heat and power generation or as fuel in vehicles. The case study illustrates that the optimal solution depends on the objective and assumptions regarding the background system--illustrated with different assumptions regarding displaced electricity production. The article shows that it is feasible to combine LCA methodology with optimization. Furthermore, it highlights the need for including the integrated waste and energy system into the model.

Challenges when performing economic optimization of waste treatment: a review

Strategic and operational decisions in waste management, in particular with respect to investments in new treatment facilities, are needed due to a number of factors, including continuously increasing amounts of waste, political demands for efficient utilization of waste resources, and the decommissioning of existing waste treatment facilities. Optimization models can assist in ensuring that these investment strategies are economically feasible. Various economic optimization models for waste treatment have been developed which focus on different parameters. Models focusing on transport are one example, but models focusing on energy production have also been developed, as well as models which take into account a plants economies of scale, environmental impact, material recovery and social costs. Finally, models combining different criteria for the selection of waste treatment methods in multi-criteria analysis have been developed. A thorough updated review of the existing models is presented, and the main challenges and crucial parameters that need to be taken into account when assessing the economic performance of waste treatment alternatives are identified. The review article will assist both policy-makers and model-developers involved in assessing the economic performance of waste treatment alternatives.

Future waste treatment and energy systems – examples of joint scenarios

Development and use of scenarios for large interdisciplinary projects is a complicated task. This article provides practical examples of how it has been carried out in two projects addressing waste management and energy issues respectively. Based on experiences from the two projects, recommendations are made for an approach concerning development of scenarios in projects dealing with both waste management and energy issues. Recommendations are given to develop and use overall scenarios for the project and leave room for sub-scenarios in parts of the project. Combining different types of scenarios is recommended, too, in order to adapt to the methods and tools of different disciplines, such as developing predictive scenarios with general equilibrium tools and analysing explorative scenarios with energy system analysis tools. Furthermore, as marginals identified in differing future background systems determine the outcomes of consequential life cycle assessments (LCAs), it is considered advisable to develop and use explorative external scenarios based on possible marginals as a framework for consequential LCAs. This approach is illustrated using an on-going Danish research project.

Optimizing the supply chain of biomass and biogas for a single plant considering mass and energy losses

Abstract The share of renewable energy in the Danish energy sector is increasing and the goal is that biogas production should reach a production level of 17 petajoules (PJ) in 2020 according to the Danish Energy Agency. However, this goal is currently not reachable due to lack of investments in biogas plants. In this paper, a mixed integer programming (MIP) model for finding the optimal production and investment plan for a biogas supply chain is presented to ensure better economy for the full chain hopefully stimulating future investments in biogas. The model makes use of step-wise linear functions to represent capital and operational expenditures at the biogas plant; considers the chain from the farmer to the end market; and includes changes of mass and energy content along the chain by modeling the losses and gains for all processes in the chain. Biomass inputs are scheduled on a weekly basis whereas energy outputs are scheduled on an hourly basis to better capture the changes of energy prices and potentially take advantage of these changes. The model is tested on a case study with co-digestion of straw, sugar beet and manure, considering natural gas, heat, and electricity as end products. The model finds a production and investment plan for a predefined location of the plant within half an hour of central processing unit (CPU) time. The resulting project turns out to be profitable and gives a production plan for each process, which underlines the possibilities of optimizing the processes in a biogas project.

The climate footprint of imports of combustible waste in systems with high shares of district heating and variable renewable energy

This work addressed the role of waste-to-energy (WtE) within the growing paradigm of the circular economy (CE), by combining long-term co-optimization of waste management and energy systems, to determine possible economic and climate impact consequences of future WtE capacity utilization. Co-optimization was realized by integration of a network optimization model for the waste sector, OptiFlow, with the partial equilibrium energy systems model Balmorel. The modelling framework allows to determine the effects of waste-derived energy production within energy systems, including induced and avoided energy (production and long-term investments). The article documents the application of this framework to an analysis of waste trade for WtE between European countries in the base year 2014 and prospectively until 2035, taking Denmark as example for an importing country. Results indicating present and long-term economic benefits for waste trade, under socio-economic conditions, were documented in a concurrent publication. Here, a broader consequential LCA approach was employed to appraise climate change impact potential in a variety of foreground and background conditions. We find that in 2014, trade of residual combustible waste was mostly beneficial from a climate perspective, as the Danish energy system still relies partly on fossil fuels. Towards 2035, climate advantages are uncertain and dependent on avoidance of higher impact waste management (i.e. sanitary landfilling), the differences in the energy carbon-intensity of importing and exporting countries, impact of global biomass supply, and the type and quantity of traded waste. In general, benefits from waste-derived energy production will be offset by direct combustion emissions as background systems decarbonize. Waste transport played only a minor role in the outcome. The study showcases integration of ESA in waste LCA to better account for affected (often referred as marginal) energy production.

The economic value of imports of combustible waste in systems with high shares of district heating and variable renewable energy

This study analyses the socio-economic value of trade of combustible waste, taking Denmark as an example for importing countries with large district heating networks and already high shares of variable renewable energy. An integrated systems analysis framework allowed to assess under which circumstances import of wastes leads to less expensive waste management and energy, accounting for increasing ambitions for a circular economy and renewable energy. The dynamics of both systems are captured through two optimization models, which are solved simultaneously. OptiFlow optimizes Danish waste management and transport, and Balmorel, the Northern European energy system. Results show that waste import to cover the existing Danish incineration overcapacity during wintertime has definite economic value. Conversely, summertime import can have negative value unless a gate fee is received, with the exception of imports of waste with high calorific content (>16.2 GJ/t). In some cases, mothballing of up to 14% of the existing incineration plants is a cost-efficient alternative to decrease the level of over-capacity. In the longer term, results show a socio-economic value of importing waste, being mainly sensitive to assumptions regarding biomass prices and wind power cost, as the technologies would compete with incineration plants. The present methodology can be applied to other countries where waste-to-energy participates in district heating, and where variable renewable electricity and constraints on biomass resources are becoming important. A pan-regional approach regarding waste management planning to maximize the value from combustible waste might be desired, along with a coherent taxation to avoid competition based on tax differences.