Year: 2010
Type: report
Abstract: The focus on global warming and security of resource supply has led many sectors in society to look for alternatives to oil and other fossil resources. Biological resources – biomass in brief – is at present a preferred alternative in many sectors of society. Biomass is, thus, in growing demand for heat and power services as well as for transportation fuels and as feedstock for chemicals and materials – i.e. in practice all sectors today being dependant on fossil fuels. At the same time, unfortunately, the food sector is also in growing demand for agricultural crops. World population is still growing and even more importantly, the composition of food is changing towards more meat on the menu, especially in the many countries in economic transition towards higher welfare; i.e. China, India, Malaysia, Indonesia, South Africa, Mexico, Brazil and more. Even without the new customers for biomass, this alone puts pressure on agricultural land and leads to new land cultivation. A look at proportions of biomass resources compared to the new customers, thus, shows that there is very far from enough for all. The world has already had an early warning in terms of potential influences from excessive biomass demand on food prices, namely the food crisis in 2007 – 2008. During this period, market prices on food and feed crops increased by almost a factor of 2, and the part of the world population suffering from hunger and starvation increased from 800 million to 900 million people. The amount of biomass that the world can sustainably use is, therefore, concluded to be small compared to the potential demand for it. The problem is that a fossil free society implies a set of conditions that make biomass in high demand: biomass can be stored and thus provide flexibility in electricity production, it can be converted to high-density fuels for mobility purposes, and it is a key source of carbon feedstock All in all, everything points to the fact, that biomass (and agricultural land) may be a severe bottleneck in the fossil free society and that excessive use can have severe consequences for the world’s forest resources, the food sector and the poorest part of the world population. We can, however, break this bottleneck. First of all, we must seek further energy savings. Secondly, we need to look for ways to de-carbonize society. There is a growing consensus among energy scientists and energy planners that society is heading towards increased electrification. The transport sector shall to the widest possible extent run on electricity and domestic and district heating shall be converted to heat pumps to the extent possible. This will help pulling more wind and solar power into our systems, and it will help balancing electricity supply and demand from fluctuating sources, because electricity is then stored in the batteries of the car fleet and in reservoirs for heating. Further electricity buffering can be provided by water reservoirs for hydro power or by various means of pressure based reservoirs, and smart grids and international trade will further assist in the balancing. But these measures are not enough. We still need high density fuels especially for aviation, but to some extent also for long distance, heavy transport on road and for sea transport. We also need carbon feedstock for our chemicals and materials. Finally, some amount of storable fuel for providing flexibility on the supply side of our electricity systems will be a big advantage. Looking at proportions in how much biomass is available without influencing the food sector shows that we have far from enough even for these priority customers alone. We need to do something to reduce our demand for biomass further. Using hydrogen as an agent to capture the electricity from wind and solar power through electrolysis is an obvious route to follow. This is judged to be a significant part of the solution. But storing and transporting hydrogen is not easy, and due to this it may be attractive to use hydrogen as an intermediate energy carrier for the final production of carbon based fuels and feedstock. In this way, using hydrogen to upgrade and recover carbon from biomass may well be the final keystone for the successful fossil free society. Through a process called hydrogenation it is possible to use biomass as a source of carbon and react hydrogen with it to produce hydrocarbons of much higher energy content and energy density than the original biomass. Moreover, using the biomass and the biogenic carbon from hydrogenation in central applications like heat and power, it is possible to collect the CO2 from the biomass and further recover and recycle it in a process here called Carbon Capture and Recycling, CCR. This will further multiply the use of the biogenic carbon from the biomass. Overall, upgrading and recycling biogenic carbon by hydrogenation and CCR, can approximately five-double our biomass potential for providing storable and high-density fuels and carbon feedstock compared to the presently applied technologies for converting biomass to fuels and feedstock. This can fully and effectively break the biomass bottleneck of the fossil free society. In this way, wind and solar power can save nature and land for food production. Assuming the next generation 6 MW wind mill, it is found that one off-shore wind mill can save 5 km2 of nature or agricultural land equivalent to 2500 tons of food crop kernels per year equal to the average calorific intake of food for 10000 people In a Danish fossil free society we seem to lack 160 PJ of biomass residue. We could import this or produce energy crops ourselves, and for the purpose we would need 8000 km2 of arable land equal to 30 % of Danish agricultural land. Or we could follow a wind-for-biomass strategy and put up 1600 off-shore 6 MW wind mills and create the 160 PJ extra biogenic fuel and feedstock by hydrogenation and CCR. By doing this, we would then save these 8000 km2 of nature or agricultural area and food production equivalent to the calorific food intake of 16 million average world citizens. The cost of CCR is greater than the fossil fuels of today, but the extra cost of it still only amounts to around 2-3 % of Danish GDP. In this cost estimate, the benefits of ultimately ensuring supply security of energy and chemical feedstock, ultimately reducing greenhouse gas emissions, avoiding food crises due to excessive use of land for energy crops, and avoiding cutting down virgin forest are not included. A road map to the sustainable use of biomass and land for energy and material feedstock purposes should be developed. In doing this, we should aim at using biomass residues only, i.e. co-products and wastes deriving from food production, forestry, industry, households, etc. We should distinguish between residues types and respect the special compositions and contents of these in terms of carbohydrates, nutrients (especially phosphorus), and proteins. It is tempting to conclude that manure and other wet residues should be reserved for biogas, and that the biogas should subsequently be hydrogenated and stored in the natural gas grid. Wooden, mainly carbohydrate containing residues should be hydrogenated to upgrade their energy content and quality up front. And care should in general be taken to use biogenic carbon at central applications as a first case allowing for a subsequent capture and recovery of the biogenic carbon. When finally converted to transport fuels, the carbon is lost with photosynthesis as the only subsequent way of recovery, and photosynthesis is unfortunately very slow in comparison.
Author: Henrik Wenzel
Language: English
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W2182668513