Reports within the energy research area

Solar collectors can give an attractive energy contribution as part of a heating system with heat pump and borehole storage, where they can provide a useful contribution even at very low temperatures. The simulation of combined solar/heat pump systems requires a dynamic collector model that can handle operation at temperatures below the dew point of the ambient air.

A model of unglazed solar collectors which also supports operation under condensation conditions has been validated by this work. The validation has shown that the model can predict the heat exchange of an unglazed solar collector very well.

The model is an extension of the dynamic collector model used in the test standard EN12975 for solar collectors, which is also available as Type 136 in the simulation tool TRNSYS.

The validation has been carried out with test data from the Swedish National Testing and Research Institute, SP, who supplied the test rig and performed the test during the period September to October 2010.

The collector model has been implemented in the system model developed by ÅF in the simulationm tool IDA ICE, for the purpose of simulation and design of local energy supply centrals based on borehole storage and heat pumps.

10-050 Local Energy Supply..

The project has achieved the stated main objectives and all milestones except the last part of the fourth milestone: demonstration of 100kW machine with high efficiency. With this goal we are working further on with the extension project, "Flywheel as power handling system and energy storage'".

08-065 Effekt och energilager

Biogas is one of the greenhouse gas neutral energy sources. Its production has developed from using relatively simple substrates, e.g. manure, towards more complex mixtures such as industry wastes products. However, intensive utilisation of these more energy-rich substrates may result in less stable process conditions with foaming and suboptimal use of the organic material. To run these process conditions at high efficiency (high organic loading with a high volatile solids reduction and at shortest possible retention time while keeping process stability) an active and fast growing microflora is crucial. It is therefore important to increase our understanding regarding microbial composition and interactions within these complex digestion webs. In the present study we map the microbial composition of 22 Swedish full-scale biogas digesters treating different substates (slaughterhouse-, municipal household- and industrial process waste, energy crops and sewage sludge) and process configurations by using the FLX genome sequencing. The obstained microflora patterns are here presented on genus level and discussed in leation to substrate composition. 

09-256.pdf

Currently biofuels have strong political support, both in EU and Sweden. The EU has, for example, set a target for the use of renewable fuels in the transportation sector stating that all EU member states should use 10% renewable fuels for transportation by 2020. Fulfilling this amibtion will lead to an enormous market for biofuels during the coming decade. To avoid increasing production of biofuels based on agriculture crops that require considerable use of arable area, focus is now to move towards more advanced second generation (2G) biofuels that can be produced from biomass feedstocks associated with a more efficient land use.

09-410 Research and development challenges

The incentives for burning alternative fuels in lime kilns are growing. An increasing demand on thorough investigations of alternative fuel impact on lime kiln performance have been recognized, and the purpose of this project has been to develop a lime kiln CFD model with the possibility to fire fuel oil and ligning. The second part of the project consists of three technical studies. Simulated data from a one-dimensional steady state program has been used to support theories on the impact of biofuels and lime mud dryness.

07-264 Lime Kiln Modeling CFD

In this project different oxygen carriers for the technology chemical-looping with oxygen uncoupling (CLOU) have been investigated. This process is highly efficient for combustion of solid fuels with inherent CO2 separation. The combustion process can be divided into three steps performed in two reactors. In the air reactor, a reduced metal oxide reacts with the combustion air to an oxidized metal oxide (Step 1). The metal oxide is then transferred to the fuel reactor, where the metal oxide decomposes and releases oxygen in the gas-phase (Step 2). Finally, the oxygen reacts with the fuel through normal combustion to a concentrated stream of CO2 and H2O. Since pure CO2 is obtained after condensation of the steam, the technology is highly applicable for CO2 sequstration. In this project a number of different oxygen carriers based on mixed metal oxides have been investigated with respect to their feasibility for CLOU. More specifically, oxygen carriers of Cu-Zr, Mn-Fe and Mn-Cu were produced through freeze granulation and investigated in a fluidized bed reactor under different conditions. In the first part of the project a screening of the different particles was made with the oxygen release properties and reactivity towards metahne investigated. From this study it was found that all of the materials were able to release oxygen in the gas-phase, albeit the extent was very deptendent on tempature. The most promising system was found to be the Cu-Zr and Cu-Mn. Because no prior investigations of the Cu-Mn materials for CLOU had been performed it was decided to pursue this further. Experiments with materials of different compositions found that even very small amounts of Cu in the Mn-matrix has a pronounced effect on the oxygen carrier behavior, and the material is very promising at temperatures of 750-825^o  C.

08-184 Combustion of solid fuels with separation of carbon dioxide

Hydrogen MacroSpheres is a novel higly efficient concept for storage and transport of Hydrogen gas. The idea is to store the gas under very high pressure (1000 bar) in many small spherical tanks, the MacroSpheres. Each tank is completely autonomus with an internal  micromechnical device a chip which is handling the gas flow to and from the tank. The gas flow is pressure controlled, at atmospeheric pressure the tanks are leak tight. At at slightly elevated pressure the tanks start to leak gas. An integrated pressure regulator stops the gas flow at a for the consumer preset working pressure.

The system combines the best storage performance availalbe (11-18 wt%) with focus on a conventient and non-dramatic handling for the user. The project has focused on some important development areas.

A bond burst equipment used for development of the microchip. The chip consists of five silicon wafers bonded together to a stack. Multiple wafer bonding is a well known problem area and a testing tool has been missing up to now. The other activity in the project was to investigate different design concepts for the small high pressure composite tanks, which has been done. The conclusion is to start with aluminum tanks for the biogas track and later shift to a high performance termo plastic LCP (liquid crystal polymer) reinforced with Kevlar for safe failure modes and a low manufacturing cost.

08-198 Hydrogen MacroSpheres

The project addressed the physical properties of thermal plasmas. It aimed at the synenergy of expertimental and theoretical analysis in order to explain the radiation transport under extreme conditions in modern plasma torches.

By application of a thermal plasma based system to a wide range of possible feedstocks which are CO2 neutral, a clean syngas of high caloric value was produced simultaneously with a non-leachable vitrified lava. The results provided the advanced technology for clean electricity by processing waste and biomass. The driving force behind the project was to give priority to the environmental quality at affordable cost. Thus, the investigation of ways to increase the efficiency of the process turned out to be very important.

The major steps in the project were: the realisation of an efficient system for clean and efficient thermal plasma based waste treatment using a plasma torch and testing the combines system for various feedstocks, including oil shale and wood stocks. The economy of the system depends mostly on a crucial parameter to determine the future of this technology. The optimistic scenario holds the promise to provide 10-15 % of the energy needs for the EU.

07-227 Plasma based total treatment

This report describes three different simulation models of plants using a ground source heat pump adapted for the IDA simulation environment (developed by Equa). The first plant is a simple baseline model using a heat pump and a grid of boreholes as main components. The second plant is based on the first one using additional dry coolers to allow the heat pump to function as a chiller when the available cooling power from the boreholes isn't sufficient. When needed, the surplus heat can be returned to the bore hole grid. The third plant studied, is based on the first one using an additional pool-type solar collector.
To better account for the differences of the systems, they are used in a case study using a borehole grid of 600 holes. Hence, the plants are quite big and are assumed to supply a total amount of 30 GWh heating and cooling. The plants are studied using two different load profiles, one where the need for cooling is 80 % of the heating demand and one where the need for cooling is only 20% of the heating demand.
One important issue when using ground source heat pump systems is the supply temperature to the secondary cooling units. Two different temperatures are used in the case study, supply temperatures of 12^o C and 18^o C respectively. For both cases, the tempeterature rise is 4^o C.

It might be dangerous to make generalizations based on the results from the case study. However, the need for electricity to powering the pumps is about 30 % of the electricity to the compressors and for every GWh put into the system four to six times of it could be utilized.
The most urgent task is to increase the speed of calculation. To accomplish this, amore time efficient model of the borehole grid is necessary. In this report, a small study is presented regarding the speed of calculation. In the study, the borehole grid is removed and replaced by a heat exchanger controlled by a sine curve. By doing this, it is possible to account for the part of the simulation speed that is governed by the borehole grid. According to this very preliminary study, the calculation speed might be about 4 minutes per year when using av very efficient model of a borehole grid.
Additionally from this preliminary study, one might draw the conclusion that this simplified model is good enough to use when performing whole year energy simulations required by the government to receive a building permit. To use a more detailed model will probalby not give a more accurate resultat when comparing the calculated energy use to the measured result.

06-111 Systemmodell för dimensionering och optimering av energicentral med borrhålslager

The project main focus has been to study the new soft materials for fuel cells.

07-181 Nya mjuka material för bränsleceller

The growing interest in biofuels and the urgent need to decrease the import dependence in the transport sector has created a debate about what biofuel to choose and how efficient different biofuels can be produced. There has been a boom in studies calculating the energy efficiency, or energy balances, for different fuels produced by different raw material. The results from these studies are, however, rarely directly comparable, due to differences in assumptions made.

In this project a number of energy balances presented in different reports are presented, discussed and analysed. The reports analysed are: Well-to-wheels (2007), Ahlvik och Brandberg (2001), Blinge et al. (1997), Heyne et al., (unpublished), Vander Meijden et al. (unpublished) and Ekbom et al. (2005).

The results from the reports have been compared as is, and then recalculated with similar assumptions to be able to analyze the differences between the results further. In some cases it was clear that is was the assumptions that differed between the studies. In other cases the differences were even greater after recalculations. Hence the results are hard to interpret.

In any case the discussions and recalculations of the result may service as a basis for anyone trying to analyze the energy efficiency of different biofuels.

08-215 Energy balances for biofuel production

In order to reach the EU-target of 10 % of renewable energy in the transport sector approx. 10 TWh will be needed in Sweden. This report presents one possible renewable fuel which can contribute to reaching this target, the Fischer-Tropsch (FT) diesel, which can be synthesized via a biomass gasification route. The objective of this report has been to investigate the prerequisites for raw material, the technology, the economy and the market concerning production of FT-diesel in Sweden. The FT-process is well-tested and commercial when the feed is coal or natural gas, however the synthesis of FT-fuels via gasification of biomass is not (yet) a commercially proven technology. Possible biomass feeds are all sorts of forest and agricultural based biomass, which are abundant in Sweden but the consumption in competing  sectors is high. Studies of the potential of increased biomass usage show that enough biomass will probably be available to reach the 10 % EU-target. A location close to process industries, such as pulp and paper mills and oil refineries, or a district heating network contributes to enhanced economies. A final upgrade of the FT-product in an oil refinery and use as a blending component in diesel and gasoline will lower production costs. This is also an efficient way to introduce FT-fuels, which can be directly integrated into the existing fuel system and require no change of engines or vechicles. However, three main obstacles have been identified, being: (1) the technology for gasification and gas cleaning needs to be proven in demo-scale, (2) large plants are needed, due to economies of scale, to give profitable production and (3) uncertainties about future policies, due to the fact that renewable will rely on exemptions from energy and COs-tax at current price levels.

09-388_fischer-tropsch.pdf

The corrosion resistance for a number of
metallic and polymeric materials, in the
environment of the inlet part of a flue gas
condenser for a combustion plant, has been
investigated. The combustion plants have been Igelstaverket and Bristaverket, for which the fuel has been mainly waste wood and biofuels,
respectively. The materials were exposed in the dry and the wet zone, and also in the transfer
zone in between. The metallic materials where stainless steels of the grades 17-10-2L, 2205, SAF2507
and 254SMO, all with a through weld joint, while the polymeric materials where fibre reinforced
plastics (FRP) and glass-flake applied on carbon steel. The FRP materials had been formed partly by
a traditional method and partly using new types of reinforcement materials, mainly based on carbon
fibre, which where located in the surface layer. Also laminate with the special reinforcement of
the type 3D-fabric was investigated. The investigation showed that all the metallic materials came
off good under normal operating conditions when using biofuels, while 17-10-2L did not manage
when using waste wood. The welds of 2205 showed a somewhat restricted corrosion resistance,
otherwise being the best choice for waste wood plants when taking the material cost into
consideration. FRP, as it seems, can be used successfully in the environments studied for
combustion plants using bio fuels. The results also indicate that the lifetime can be improved and
the maintenance reduced by doing the correct choice of laminate structure and material
compared to the laminates of the common type. The laminate structure, however, has to be
adjusted to fulfil the demands given by the process environment. It should also further be pointed
out that the good results for the flake coatings not necessarily would be the case for real use,
where the walls are exposed to a temperature gradient. Finally, a conclusion, outside the initial
purpose of the project, was that the addition of ammonium sulphate in Bristaverket in accordance
with ChlorOut, contributed to the heavy coatings formed in the inlet part of a flue gas condenser
of Bristaverket.

06-266_korrosion_i_rokgaskondensor.pdf

Three different types of making realistic
examinations of water side corrosion for
combustion plants exist - by using a loop, by
using an autoclave and by doing in situ
measurements. If using a loop, the exposure
of the sample can be made very realistic, and the environment can be held under strict control and at the same time be changed towards extreme characteristics. No loops for doing investigations of
water side corrosion is however available in Sweden. The focus was therefore on the testloop, by
ascertain the different variations of construction possibilities and the cost. The cost of building a
loop capable of doing measurements at extreme pressures e.g. 200 bar, is however very high. A level
of 1.3 million SKR is not an understatement and the cost of operating is also not low, e.g. 20 000
SKR per month for a measurement on a tube with an inner diameter of 2.5 cm, a flow rate of the
tube water of 0.5 m/s and having a pressure of 200 bar. It is a cost that can be overcome though, if
some sort of cooperation is made. Doing measurements by using an autoclave is less expensive but
far less realistic due to that no heat gradient occurs through the sample, due to no risk of boiling
and therefore increase of water soluble species concentrations and due to no erosive effects from
the water flow. Doing in situ measurements by changing the plant tubes are even less expensive,
but the exposure environment can not be varied as much as wanted because of the plant safety.
However, all three methods have their own advantages and can be of useful complement to each
other when trying to increase the knowledge of waterside corrosion and how to attain a good
magnetite layer.

06-264_vatskesidiga_panntubsprocesser.pdf

The purge of chloride and potassium from the chemical recovery cycle will be of increased importance in the future since a new generation of high-pressure recovery boilers will be taken into operation in Sweden within the next few years. In order to successfully purge these two salts, the solubility of an aqueous salt mixture containing Na₂SO4 – N a2CO3 – NaCl – NaOH – KCl – K2SO4 – K2CO3 – Na2S must be know. The present knowledge in this matter is incomplete.

This study aims to summarize the present knowledge on salt solutions and point to areas of further research.

A number of conclusions can be made form the material collected for this study. Based on the conclusions in this study, the following future research activities are recommended.

05-078_syntesrapport.pdf

The study analysis prerequisites for ethanol production from wood in Sweden with concern to market issues, production methods, raw material supply and current usage of requested raw material assortments.

From a Swedish perspective, cereals, sugar beet and several cellulosecontaining materials as straw, energy forest and wood are possible raw materials. At an early stage, Swedish research focused on wood, with branches and tops, as the primary resource for ethanol production. The R&D has so far only tested purer materials as wood chips and saw dust. Research progress within fermentation of pentose sugars, minimising water flows, optimising byproduct usage and integration concepts are also needed before large scale plants can be built.

The raw material competition is increasingly fierce with several sectors (pulp and paper, energy, saw mill, board producers and biofuel) competing for wood raw material. Our analysis indicates a raw material potential of 5 TWh (branches and tops) could be available for ethanol production under two conditions; an increased take-out of forest residues and usage of new raw material assortments from agriculture and forest. 5 TWh raw material corresponds to approximately 350 000 m3 ethanol. The EU biofuel directive recommends a substitution of fossil vehicle fuels of 5,75% and 10% 2010 respectively 2020. If these figures where to correspond to ethanol, 760 000 respectively 1 400 000 m3 ethanol will be needed. Thus, wood raw material cannot fully substitute fossil fuels without using assortments already used by other sectors.

Today, Swedish ethanol production (wheat) is expensive in comparison to production based on other raw materials as sugar cane or molasses. The reasons are lower cost for raw material and labour. Today, the custom duty on ethanol from countries outside is a condition for profitability of Swedish production. The Swedish government are currently working to annull the duty, which if succeded, will cause great difficulties for Swedish ethanol producers as the competition with imported ethanol from South America or Asia will be fierce. This situation may however change if the demand and price level continue to rise.

06-279_ethanol_production_from_wood.pdf

I ett tidigare projekt sponsrat av ÅF Forskningsstiftelse (02-171) och CF Miljöfond har lämpliga syrebärare för processen ’Integrerad vätgas- och kraftproduktion’ identifierats med hjälp av reaktivitetsförsök i en batch fluidiserad bädd reaktor samt en TGA. Här identifierades system NiO/MgAl2O4 som ett mycket lämpligt system för att använda för vätgasproduktion med sk. ’chemical-looping reforming’. Målet med detta projekt var att testa några syrebärare i en mindre 300 W kontinuerligt fungerande reaktor baserad på ihopkopplade fluidiserade bäddar. Emellertid har det inte funnits utrymme att studera mer än just en syrebärare baserad på NiO och MgAl2O4. I detta projekt har en syrebärare av detta system tillverkats med frysgranulering och undersökts i den kontinuerliga reaktorn med stor framgång, och därmed har processen för första gången demonstrerats. Vidare har även en kinetisk undersökning av syrebäraren utförts i en TGA och resultaten modellerats med en enkel gas-fastfas modell. Två publikationer har skrivits inom projektet, och dessa finns med i appendix till rapporten.

05-197_integrerad_vatgas-_och_kraftproduktion....pdf

PV-modules based on crystalline silicon are often purchased with a warranty of 25 years. The modules that are tested and approved according to the IEC 61215 standard are considered to have an expected lifetime of 20-30 years. Although the tests are designed to simulate the stresses that modules are exposed to in real operation, it is not until analyses are made of modules that have been in operation for many years that definite statements about module lifetime can be made. Today more and more systems are approaching these long lifetimes and thereby providing us with true examples of module lifetime.

Elektroporation för forcerad och hygienisk metanutvinning

07-156_long_term_pv_performance--results_from-_swedish_case_studies.pdf
07-156_poster.pdf

The profitability of anaerobic digestion of energy crops is limited mainly because of low methane yield, long retention time and costly disinfection. The objective of the proposed project E-METAN was to accelerate biodegradation and to kill pathogens using electric pulses. The so-called electroporation was applied on sugar beets (species Opta) and E-coli. The effect on the kinetic as well as the potential of methane formation was investigated using BMP assays (Biochemical Methane Potential). The reduction in E-coli concentration was determined. Comminuted sugar beets resulted in a methane formation potential yielding 5,05±0,06 kW ha-1 whereof ~55% were due to easily degradable matter. Electric pulses increased the accessibility for degradation. The methane formation kinetic and the methane formation potential increased with 16% and 27%, respectively. The effect of electroporation on disinfection was insufficient at the maximum applied field strength of 24 kV cm-1.

06-127_e-metan.pdf