Per-Anders Hansson

Emissions from fuel combustion in Swedish cod fishery

This study presents emission data (CO2, NOx, CO, HC and SOx) for fishing vessels, calculated per kg of cod landed by Swedish fishermen. Three scenarios are included; one reflecting the fishery and fleet of 1999, one assuming modern engine technology and, finally, a future scenario assuming a slight increase in the use of passive gear (seines and long-lines) and pair trawls instead of single trawls, lower fishing effort and lower emission levels. The effects on the results of different allocation strategies for landed by-catches are evaluated. Data was gathered from official fishery statistics and engine emission data from one of the major manufacturers of marine diesels. Fuel consumption data for otter trawling and gillnet fishing was obtained by having fishermen fill out a questionnaire. The results include emission calculations for gillnet fishing and trawling, and indicate lower emissions per kg of cod caught for gillnet fishing, due to lower fuel consumption. Considerable options for decreasing fuel consumption and emissions produced in cod fisheries through changes in technology and fisheries policy were concluded from this work. Choosing allocation method was shown to be important for the final results, especially in mixed, high-value target fisheries.

Ammonium nitrate fertiliser production based on biomass - environmental effects from a life cycle perspective.

Ammonium nitrate and calcium ammonium nitrate are the most commonly used straight nitrogen fertilisers in Europe, accounting for 43% of the total nitrogen used for fertilisers. They are both produced in a similar way; carbonate can be added as a last step to produce calcium ammonium nitrate. The environmental impact, fossil energy input and land use from using gasified biomass (cereal straw and short rotation willow (Salix) coppice) as feedstock in ammonium nitrate production were studied in a cradle-to-gate evaluation using life cycle assessment methodology. The global warming potential in the biomass systems was only 22-30% of the impact from conventional production using natural gas. The eutrophication potential was higher for the biomass systems due to nutrient leaching during cultivation, while the acidification was about the same in all systems. The primary fossil energy use was calculated to be 1.45 and 1.37MJ/kg nitrogen for Salix and straw, respectively, compared to 35.14MJ for natural gas. The biomass production was assumed to be self-supporting with nutrients by returning part of the ammonium nitrate produced together with the ash from the gasification. For the production of nitrogen from Salix, it was calculated that 3914kg of nitrogen can be produced every year from 1ha, after that 1.6% of the produced nitrogen has been returned to the Salix production. From wheat straw, 1615kg of nitrogen can be produced annually from 1ha, after that 0.6% of the nitrogen has been returned.

Influence of various machinery combinations, fuel proportions and storage capacities on costs for co-handling of straw and reed canary grass to district heating plants

Abstract Autumn-harvested cereal straw and spring-harvested reed canary grass (Phalaris arundinacea L.) are renewable energy sources with similar material characteristics. The fuels can be harvested and handled with the same machines, stored in the same stores, and fired with the same equipment. Thus, there is a possibility to reduce costs and increase supply reliability at many locations by using reed canary grass (RCG) as a complementary fuel in straw-fired district heating plants. The objective of this study was to find appropriate machinery combinations, straw/RCG proportions and storage capacities in order to reduce the total costs of the fuel system. The tool for the analyses was a modified dynamic simulation model for straw handling called SHAM (Straw HAndling Model). To include handling of RCG, SHAM was extended with submodules for calculation of daily fuel use, soil moisture contents and early crop growth. The model was applied to a fictitious heating plant in Enkoping in central Sweden as a case study. The simulations showed that the total costs can be lowered by using both straw and RCG in suitable proportions instead of solely using straw, although the primary fuel cost for RCG is more than three times higher per GJ than for straw. The choice of reserve base load fuel had a significant impact on the results, particularly when the RCG proportion was small, because the consumption of the reserve fuel became proportionally higher in such cases.

Greenhouse gas balance of harvesting stumps and logging residues for energy in Sweden

Abstract In this case study, forest fuel procurement chains of stumps and logging residues were evaluated using a Life Cycle Assessment perspective. Direct emissions from combustion were not included, but soil organic carbon change was included as changes in carbon stocks in litter and soil. The results showed that primary forest biomass for energy has a climate impact which is time dependent. However, in long-time perspectives, there are large greenhouse gas (GHG) savings. In a short-term (20 years), there were no GHG savings when natural gas or coal was replaced. This is due to the fact that the harvest lead to decreased input of organic matter to the soil which is compared to a reference where biomass are left to decompose. The reduction in soil organic carbon may have been underestimated in the stump harvest systems studied, as the effect of soil disturbance per se was not included. Important factors when assessing GHG balance of forest fuels, besides the time horizon used, were site productivity, geographical position and forest fuel resource (stumps or logging residues). When assessing the greenhouse gas savings, efficiency of the end-use, allocation method between heat and power and type of fossil fuel replaced were also important.

Analysis of field machinery performance based on daily soil workability status using discrete event simulation or on average workday probability

Abstract The objective of the study was to develop a simulation model for field machinery operations using a discrete event simulation technique in order to analyse machinery performance based on daily status of soil workability for a series of years ( Daily Work . method), and to compare the results with those from a simpler method based on average probability values of available workdays for operations and seasons ( Aver. Work . method). Timeliness costs with this latter method were estimated using the formula proposed by ASAE Standards, ASAE EP496.2 DEC99. Seven machinery sets were assessed on a 400 ha farm with both methods in terms of total costs (labour+specific machinery+timeliness costs) to find the effect of the methods on assessment of timeliness costs. The model for field machinery operations was developed in the Arena simulation language, allowing simulation of field operations on a real farm for a 20-year period. Completion dates of operations in individual fields were important outputs of the model, which enabled timeliness costs to be estimated in detail. Daily soil workability was inferred by means of moisture thresholds from simulated soil moisture contents from another model (the SOIL-model) and weather data from Uppsala, Sweden. The validity of the machinery model was tested with data from a farm, the daily results of the model had good agreement with the progress of the field operations at the real farm. The assessment of the seven machinery sets revealed that machinery costs were the main component of total costs and, as expected, they increased with machine size. Labour costs and timeliness costs decreased as machine size increased with both methods. The Aver. Work. method estimates resulted in lower timeliness costs for sowing operations than those determined with the Daily Work . method, which was attributed to the fact that former method did not take into account chain effects. Regarding timeliness costs for harvesting operations, the Aver. Work. method was considered inappropriate because of scattered field maturity times in the region of the study where single periods with their own optimum time are difficult to identify. In addition, the ASAE formula was very sensitive to the number of such periods. In contrast, timeliness costs with the Daily Work . method were estimated for sowing and harvesting operations taking into account some management criteria and chain effects were captured on a field basis. They were quantified for sowing and harvesting operations based on a long-term assessment (20 years) and their yearly variability was determined.

Energy- and exergy analysis of rape seed oil methyl ester (RME) production under Swedish conditions

Abstract In this study the rape seed oil methyl ester (RME) production chain was analysed with respect to its energy- and exergy efficiencies. The differences between results from an ordinary energy analysis and an exergy analysis of the production were also quantified and discussed. The sensitivity of the results to changes in some of the most important input parameters were then analysed in order to find production strategies that increase the exergy efficiency. The study was applied to rape seed cultivation situated in southern Sweden. The rape seed oil was hot pressed in a large-scale plant, and the RME was esterfied in the same factory as that in which in the rape seed oil was pressed. Both direct and indirect energy and exergy flows used for RME production were included. The analysis showed that a large part of the energy and exergy used to produce RME was related to nitrogen fertilizers and diesel fuels. Another important conclusion was that the exergy efficiency of the production in general is higher than the energy efficiency. A third conclusion was that it is possible, by using alternative production strategies, to improve the exergy efficiency without decreasing the energy efficiency.

Nitrogen fertiliser production based on biogas - Energy input, environmental impact and land use

The aim of the present paper was to investigate the land use, environmental impact and fossil energy use when using biogas instead of natural gas in the production of nitrogen fertilisers. The biogas was assumed to be produced from anaerobic digestion of ley grass and maize. The calculations showed that 1 ha of agricultural land in south-west Sweden can produce 1.7 metric ton of nitrogen in the form of ammonium nitrate per year from ley grass, or 3.6 ton from maize. The impact on global warming, from cradle to gate, was calculated to be lower when producing nitrogen fertiliser from biomass compared with natural gas. Eutrophication and acidification potential was higher in the biomass scenarios. The greatest advantage of the biomass systems however lies in the potential to reduce agricultures dependency on fossil fuels. In the biomass scenarios, only 2-4 MJ of primary fossil energy was required, while 35 MJ/kgN was required when utilising natural gas.

Life cycle assessment of energy self-sufficiency systems based on agricultural residues for organic arable farms

The agricultural industry today consumes large amounts of fossil fuels. This study used consequential life cycle assessment (LCA) to analyse two potential energy self-sufficient systems for organic arable farms, based on agricultural residues. The analysis focused on energy balance, resource use and greenhouse gas (GHG) emissions. A scenario based on straw was found to require straw harvest from 25% of the farm area; 45% of the total energy produced from the straw was required for energy carrier production and GHG emissions were reduced by 9% compared with a fossil fuel-based reference scenario. In a scenario based on anaerobic digestion of ley, the corresponding figures were 13%, 24% and 35%. The final result was sensitive to assumptions regarding, e.g., soil carbon content and handling of by-products.

Optimization of agricultural tractor cab suspension using the evolution method

Abstract The use of cab suspensions on agricultural tractors increases the possibilities to reduce the vibration load on the driver within the limits imposed by the major constraint, i.e. the available travel space. This paper describes a model for optimization of parameters describing the characteristics of a passive nonlinear cab suspension. The optimization method is based on an evolution algorithm. The objective has been to minimize the total vibration load on the driver. The studies performed show that the method is a very useful tool for optimization of cab suspension characteristics. The absolute optima were not always found but the differences in the values of the objective function were small.

Nutrient and cost optimization of fertilizing strategies for Salix including use of organic waste products

Abstract A model was developed to minimize the grower’s costs for fertilization of Salix aimed for energy production, when a user-defined amount of organic waste products and commercial fertilizers are available. The fertilizers applied have to fulfil the nutrient demand of the crop, while the regulations on maximum heavy metal loading rates must not be exceeded. The model described is based on mixed integer programming (MIP) and calculates the optimal amount of fertilizing products to apply in each year of a four year cutting cycle. The model is general and may be used for optimization of fertilization strategies for energy crops under a wide range of circumstances. Optimal fertilizing strategies were also studied for some typical cases in order to define the characteristics of the method and to study some general trends in the results. The results showed that the use of untreated municipal waste water was very economically favourable for fertilization of Salix in cases where this product is available and where conditions are suitable for a permanent irrigation system. Another important conclusion was that the nutrient demand of the Salix crop may be met by organic products, without exceeding the Swedish limits for maximum heavy metal application rates on agricultural land. A third conclusion was that products with low concentrations of nutrients, for example biogas sludge, are economically favourable for the grower when the transport distances are short. When the transport distances increase, more concentrated products such as commercial fertilizers become more competitive.