Convention Relating to a Uniform law on the Formation of Contracts for the International Sale of Goods

Many infrastructural projects have cost overruns and there has been a lot of research both on whythese cost overruns occur and what can be done to reduce cost overruns. Bent Flyvbjerg is the leadingresearcher in the area and in this article his proposals are also the starting point. Beside a literaturereview a questionnaire was also sent out to experienced Swedish project managers to find out whatthey thought could reduce cost overruns. This has been the foundation for the proposals formulated inthis article. Proposals concerns three areas 1. Organizational macro-structure, e.g. using more PPPprojectsbut also decentralization of budgets where cost-overruns in one project in a region leads toless other projects in the specific region. 2. Organizational quality: It should be easy to see when andwhere cost overruns occur and who was responsible. There should be an well-developed knowledgemanagement system in the organization and an organization culture of openness and a focus onimprovements. 3. Organizational processes, e.g. a systematic use of external reviewers in differentstages of a project.QC 20140819</p

Policies to Avoid Cost Overruns in Infrastructure Projects: Critical Evaluation and Recommendations

Many infrastructure projects have cost overruns and there has been a lot of research both on why these cost overruns occur and what can be done to reduce hem. Bent Flyvbjerg is the leading researcher in the area and in this article his proposals are used as the starting point. Besides a literature review, a questionnaire was sent out to experienced Swedish project managers to find out what they thought could reduce cost overruns. The literature review and the questionnaire were the foundation for the proposals formulated in this article. Proposals concerned three areas: (1). Organisational macro-structure, e.g. using more PPP projects but also decentralisation of budgets where cost overruns in one project in a region lead to less alternative projects in the specific region. (2). Organisational quality: It should be easy to see when and where cost overruns occur and who was responsible. There should be a well-developed knowledge management system in the organisation and an organisation culture of openness with a focus on improvements. (3). Organisational processes, e.g. a systematic use of external reviewers in different stages of a project. Keywords: Cost overruns, Infrastructure projects, Policy measure

Opium for the Masses? Conflict-Induced Narcotics Production in Afghanistan

We show that the recent rise in Afghan opium production is caused by violent conflicts. Violence destroys roads and irrigation, crucial to alternative crops, and weakens local incentives to rebuild infrastructure and enforce law and order. Exploiting a unique data set, we show that Western hostile casualties, our proxy for conflict, have strong impact on subsequent local opium production. This proxy is shown to be exogenous to opium. We exploit the discontinuity at the end of the planting season: Conflicts have strong effects before and no effect after planting, assuring causality. Effects are strongest where government law enforcement is weak.conflict, narcotics production, resource curse, Afghanistan

Combustion of municipal solid waste in fluidized bed or on grate – A comparison

Grate firing is the most common technology used for combustion of municipal solid waste. The more recently developed fluidized bed (FB) combustion is rarely employed for this purpose. The present work compares the technical properties of the two devices to find out why FB has not been more used, considering the recent importance of waste-to-energy. Several drawbacks of FB, the need for fuel preparation and bed material consumption, play a role, but these features also have advantages: combustion is improved by the sorted fuel and less ashes. Silica sand as a bed material has the positive property of being an alkali scavenger. If replaced by an oxygen carrier (e.g. ilmenite) the scavenging effect increases, and, in addition, oxygen carriers even out the non-combusted gaseous fields in the furnace, which improves combustion and allows higher steam data at a given corrosion level. There are other advantages of FB, such as end-superheaters in the circulation loop, heated by the bed material. However, also the environmental performance and energy efficiency of grate firing has been improved, and several advanced solutions have been proposed. In conclusion, it is not clear which of the devices that is the better one. An economic evaluation is made, based on available literature information, but still there is no clear winner

EVALUATION OF FLUID DYNAMICS IN A HOT AND A COLD SYSTEM OF INTERCONNECTING FLUIDISED BEDS

Operation controllability and fluid dynamics were evaluated in a system of interconnecting fluidised beds. Results indicate that the solid circulation is controllable and possible to determine from pressure measurements. Sufficient gas tightness of the loop-seals and flexibility in controlling of solid fluxes was indicated

Validation of the oxygen buffering ability of bed materials used for ocac in a large scale cfb boiler

Fluidized bed combustion is widely considered an advantageous technology managing moist and heterogeneous fuels due to the heat storage in the bed material and its favorable conditions regarding fuel and oxygen mixing throughout the combustion chamber. Even though mixing is often regarded as sufficient, the technology remains sensitive to variations in load and heterogeneity of fuels, leading to an uneven distribution of oxygen in time and space of the furnace. The remedy has nearby exclusively been related to the supply of air, particularly considering a surplus of air and positioning of injection ports. An applicable combustion concept, oxygen carrier aided combustion (OCAC), has been developed and demonstrated in the Chalmers 12 MWth circulating fluidized bed boiler. The novelty of this concept is that it targets the distribution of oxygen inside the combustion chamber on contrary to prior accepted remedies. The rational is to replace the regularly used inert bed material by an oxygen carrying metal oxide which can take up oxygen where it is abundant and subsequently release it to combust unburned gases at oxygen depleted zones. Thus, the bed material functions as a buffer of oxygen allowing for lower surpluses of air and better ability to handle load variations and heterogeneous fuels. This work contains the modeling of a system where inert bed material is compared to an oxygen carrier with the aim to show the effects of its oxygen-buffering ability. To a system with constant fuel feed, a pulse of instantaneous fuel increase is modeled. The outcome of the model was then verified by the results of experimental work conducted in Chalmers 12 MWth CFB boiler. The results consistently show that the introduced oxygen carrying bed material does have an oxygen-buffering ability and the distribution of oxygen is considerably improved throughout the combustion chamber. Due to the enhanced distribution of oxygen the system is less sensitive to fluctuations in load and fuel heterogeneity. As the infrastructure of plants where the concept would be applicable are already in place, the use of active bed material for oxygen carrier aided combustion has great potential to reach full scale commercialization in a near future. Furthermore, naturally occurring ores that contain considerable amount of metals such as iron and manganese have proven to be promising candidates as oxygen carriers. Owing to the possibility of using natural ores, in place of manufactured materials, economic feasibility of the concept is promising

Catalytic tar cleaning of biomass-derived gas with simultaneous catalyst regeneration

Tar cleaning of raw gas from biomass gasification is a necessary operation before the gas can be used as feedstock for synthetic fuels. The technology for gas cleaning that is commercially available today (scrubber systems), is associated with problems like heat penalties and loss of the chemically stored energy within the tars. These problems are addressed in this work, and a novel method for secondary tar cleaning is proposed and experimentally validated. The method is applicable to all types of biomass gasifier and regardless of whether primary measures for tar reduction are used or not. The tar cleaning system can be thermally integrated with the gasifier outlet temperature, which leads to minimal heat losses. The method combines tar cleaning with catalyst regeneration in a system of dual fluidized beds, which in this work is experimentally explored in two identically sized reactors systems: a cold Perspex unit and a high temperature steel unit. Fluid dynamics and operation controllability was evaluated in the cold system, where the results indicated that the solid circulation is controllable and sufficient gas tightness of the loop-seals could be achieved. The gained knowledge from operating the cold system was then used to demonstrate the tar cleaning method in the hot reactor system. This was done by using raw gas from Chalmers biomass gasifier, which contained roughly 30 gtar/Nm3tar. Tar reforming activity, catalyst regeneration and the potential for catalytically adjusting the raw gas was investigated with two different catalysts: (1) Ilmenite (Fe2TiO3), a naturally occurring ore with bulk price comparable to hard coal and, (2) Mn4MgZ1150, a synthetic manufactured catalyst consisting of 40 % Manganese oxide (Mn3O4) supported on 60 % Magnesium-Zirconium oxide (MgZrO3). Experiments with 60 % ilmenite in silica sand and 23 % M4MgZ1150 in silica sand were performed. The result showed that the total amounts of tars were reduced by as much as 44.5 % in the M4MgZ1150 case and by 35 % in the ilmenite case. Both catalysts showed activity in Water-Gas Shift reaction and the H2/CO ratio was shifted from 0.7 in the raw gas to 3 downstream of the reactor system for the ilmenite case and 0.6 to 1 in the manganese case. Finally, an application for online monitoring of moisture content in a hot gas streams with rapid response time has been developed and experimentally investigated. The idea is to replace the analogous weighting system for measuring the condensate water downstream of the tar cleaning reactor, which only gives a measurement in the time period of 5 – 10 min. In this work, the method is, however, experimentally tested in the 12 MWth biomass fired CFB-boiler at Chalmers but, it can equally be used downstream of the tar cleaning reactor. The result showed that the application could detect moisture variations with a response time in the order of seconds. No sign of hysteresis was detected and very good precision in moisture content was achieved, with less than 4 % error after calibration.Key words: Tar cleaning, Catalytic gas cleaning, Biomass gasificatio

Catalytic tar cleaning of biomass-derived gas with simultaneous catalyst regeneration

Tar cleaning of raw gas from biomass gasification is a necessary operation before the gas can be used as feedstock for synthetic fuels. The technology for gas cleaning that is commercially available today (scrubber systems), is associated with problems like heat penalties and loss of the chemically stored energy within the tars. These problems are addressed in this work, and a novel method for secondary tar cleaning is proposed and experimentally validated. The method is applicable to all types of biomass gasifier and regardless of whether primary measures for tar reduction are used or not. The tar cleaning system can be thermally integrated with the gasifier outlet temperature, which leads to minimal heat losses. The method combines tar cleaning with catalyst regeneration in a system of dual fluidized beds, which in this work is experimentally explored in two identically sized reactors systems: a cold Perspex unit and a high temperature steel unit. Fluid dynamics and operation controllability was evaluated in the cold system, where the results indicated that the solid circulation is controllable and sufficient gas tightness of the loop-seals could be achieved. The gained knowledge from operating the cold system was then used to demonstrate the tar cleaning method in the hot reactor system. This was done by using raw gas from Chalmers biomass gasifier, which contained roughly 30 gtar/Nm3tar. Tar reforming activity, catalyst regeneration and the potential for catalytically adjusting the raw gas was investigated with two different catalysts: (1) Ilmenite (Fe2TiO3), a naturally occurring ore with bulk price comparable to hard coal and, (2) Mn4MgZ1150, a synthetic manufactured catalyst consisting of 40 % Manganese oxide (Mn3O4) supported on 60 % Magnesium-Zirconium oxide (MgZrO3). Experiments with 60 % ilmenite in silica sand and 23 % M4MgZ1150 in silica sand were performed. The result showed that the total amounts of tars were reduced by as much as 44.5 % in the M4MgZ1150 case and by 35 % in the ilmenite case. Both catalysts showed activity in Water-Gas Shift reaction and the H2/CO ratio was shifted from 0.7 in the raw gas to 3 downstream of the reactor system for the ilmenite case and 0.6 to 1 in the manganese case. Finally, an application for online monitoring of moisture content in a hot gas streams with rapid response time has been developed and experimentally investigated. The idea is to replace the analogous weighting system for measuring the condensate water downstream of the tar cleaning reactor, which only gives a measurement in the time period of 5 – 10 min. In this work, the method is, however, experimentally tested in the 12 MWth biomass fired CFB-boiler at Chalmers but, it can equally be used downstream of the tar cleaning reactor. The result showed that the application could detect moisture variations with a response time in the order of seconds. No sign of hysteresis was detected and very good precision in moisture content was achieved, with less than 4 % error after calibration.Key words: Tar cleaning, Catalytic gas cleaning, Biomass gasificatio

Evaluation of bed-to-tube heat transfer in a fluidized bed heat exchanger in a 75 MWth CFB boiler for municipal solid waste fuels

Bed-to-tube heat transfer has been investigated for a tertiary superheater in a 75 MWth Circulating Fluidized Bed (CFB) boiler in Norrk\uf6ping, Sweden. The boiler is used for incineration of solid waste fuels. Two fluidized bed heat exchangers are located in loop seals, connecting the cyclones and the furnace. The heat exchangers are placed in series, with respect to the steam side, and in parallel, with respect to the particle side. The total heat transfer surface area is roughly 44 m2, distributed over 72 tubes. The total effect transferred most often is in the range 2–6 MW. The incoming steam temperature in the first superheater is 380–400 \ub0C, while the exiting steam temperature from the second is around 450\ub0, at 65 bar pressure. The bed temperature in the Fluidized Bed Heat Exchanger (FBHE) is 850–875 \ub0C. The analysis is based on operational data from two time periods (2002–2005 and 2014–2021). The two periods use different heat exchanger designs, following a retrofit in 2005. The aim of the study is to establish the bed-to-tube heat transfer coefficient in an industrial FBHE unit and investigate how it varies over different time periods, for two different bed materials and for two different designs. Also, the experimentally determined heat transfer coefficients are compared with an established heat-transfer correlation, for prediction of heat transfer from bubbling fluidized bed to tubes. Operation with two bed materials were evaluated, namely silica sand and crushed and beneficiated ilmenite. Both materials are classified as Geldart B particles. Air is used as fluidization gas in the FBHE. The analysis show, with a few exceptions, comparably low heat-transfer coefficients from bed to tube of 100–150 W/(m2K). The results were similar for silica sand and ilmenite, but the highest measured heat transfer coefficient was for a period with ilmenite. The heat transfer was lower than expected based on literature data from FBHE units and fluidized bed boilers in general, and much lower than bed-to-tube heat transfer coefficients from lab-scale experiments and empirically derived predictive expressions. The difference could be related to one or more of several factors, such as the effect of very small tube spacing, unknown thermal conductivity of one of the layers in the tube bundle, the effect of lateral particle flow and the effect of fouling due to ash layers forming on the tube surfaces. It is suggested that it should be possible to significantly increase the bed-to-tube heat transfer by increasing the tube pitch, which is expected to improve bed mixing without increasing the risk of corrosion