Evaluation of techno‐economic studies on the bioliq® process for synthetic fuels production from biomass

echno-economic studies by various research institutions on the costs for the production of biomass to liquid (BtL) fuels using the bioliq® process were analyzed and evaluated. The bioliq® process consists of decentralized pretreatment by fast pyrolysis plants for biomass energy densification, and of a central gasification and synthesis step for synthesis of gas and synthetic fuel production. For comparison, specific material and energy flows were worked out for both process steps, and conversion efficiencies were calculated for the conversion of straw to diesel fuel via the Fischer-Tropsch synthesis. A significant variation of the overall process efficiency in the range of 33–46% was mainly a result of the different assumptions made for electricity generation at the central location. After breaking down the individual cost items to either fixed or variable costs, it turned out that the largest cost items in the production of BtL fuels were attributable to feedstock and capital costs. Comparison of the specific investments showed that, in addition to economies of scale, other factors had a significant influence leading to values between 1000 and 5000 EUR/kW. This, particularly, included the origin of the equipment purchase costs and the factors applied to them. Fuel production costs were found to range between 0.8 and 2.6 EUR/L. Possible cost reduction by learning potential was investigated, leading to an improvement by a few percent of production costs. A sensitivity analysis of the individual cost items by up to 30%, for “investments” and “biomass and transport” cost increases, led to higher manufacturing costs of up to 17% in both cases. By harmonizing the depreciation period and the chosen interest rate, the production costs changed from −16% to +17%. Similarly, effects could be shown by adjusting the costs for maintenance and servicing, and the plant operation time. A superposition of these effects in a best-case scenario led to cost reductions of 21%. The most expensive variant in the opposing worst-case scenario raised costs by up to 27%. This uncertainty contributed already fifty percent to a preliminary cost estimate based on a conceptual design

Influence of reactor type on production cost of fast pyrolysis bio-oil

The design of a fast pyrolysis reactor to convert biomass has a decisive influence on quality and yield of fast pyrolysis bio-oil (FPBO). Quality requirements are comparably low for the application of FPBO as gasifier fuel for subsequent conversion to synthesis gas, e.g. in the case of the bioliq® concept to convert (ash-rich) agricultural residues to drop-in, 2nd generation biofuels. Within this concept, one optimization parameter of fast pyrolysis is to maximize carbon yield in the liquid product while keeping product requirements that allow feeding into a high-pressurized entrained flow gasifier. This optimization space allows for a more flexible choice of reactor design. The aim of this study is to investigate the influence of reactor type on production cost of FPBO within above outlined framework, i.e. as feedstock for a downstream gasifier. The investigation will be based on two different type of reactors. First, a twin-screw mixing reactor (TSMR) is being considered, which resembles the actual realization of the 500 kg h-1 fast pyrolysis pilot unit that is being operated as part of the bioliq® project. Second, a fluidized bed reactor (FBR) will be compared to that, which represents state of the art technology of industrial fast pyrolysis units. One important difference between the two reactors is the necessity of a fluidizing agent in case of the FBR, which in turn influences process design and equipment size, specifically in the product recovery section. This additional (inert gas) volume flow is not required in the case of a mechanical mixing, as is the case in the chosen TSMR. At the same time it is obvious that there will be a significant difference in mixing conditions of biomass and heat carrier particles in the two types of reactors, which will translate to a difference in heating rate of the biomass particles. This in turn might affect FPBO quality and yield. Experiments have been conducted to compare FPBO yields from process development units that feature a TSMR and an FBR, respectively. No significant differences in FPBO yield have been observed. On the one hand this leads to the conclusion that the high heat transfer required to achieve one of the fast pyrolysis conditions (i.e. high temperature of primary pyrolysis inside the biomass particle) is comparable in both types of reactors. This could be explained by the high bulk density achieved during mechanical agitation as compared to that of a fluidized bed, which is capable of making up the lower mixing intensity if a proper ratio of biomass to heat carrier particles is kept. On the other hand, wheat straw (which is the ‘model’ feedstock for the bioliq® project) was used as feedstock in these experiments This choice might also lead to not observing differences between the two reactor types. Wheat straw is characterized by high ash content (around 8%) which increases the significance of secondary cracking reactions and thus lowers any effects of reactor type. Wheat straw also exhibits high heterogeneity which translates to increased standard deviation of the results (confirmed by multiple test runs) and an increased difficulty to detect differences in FPBO yield. Based on the experimental results, the effect of process design on FPBO production cost are reduced to investment and operation cost. Existing production cost calculations for the bioliq® concept have been reviewed and updated due to the currentness of the underlying data. Additionally, relevant process design changes and equipment cost will be implemented for consideration of an FBR instead of the TSMR. Finally, a sensitivity analysis is conducted to reflect changes in product yield based on available literature data for fast pyrolysis of wheat straw in order to account for the previously discussed uncertainty of the obtained experimental results

Suppressing the aromatic cycle of the dimethyl ether to hydrocarbons reaction on zeolites

The influence of the zeolite framework type on the conversion of dimethyl ether (DME) to hydrocarbons (DTH) was investigated for *MRE, MFI and TON zeolite catalysts. Remarkable differences in the catalytic performance of the materials were observed. In particular, the *MRE zeolite showed an exceptionally high yield of olefins (90%) with a substantial ratio of products in the chain length range C$_5$-C$_{11}$. Additionally, the longevity of the *MRE zeolite clearly exceeded previously reported data. The comparison of mechanistic parameters (Hydrogen-Transfer-Index HTI$_{Ci}$ and C$_3$/C$_2$ ratio) demonstrated for this zeolite, that the formation of aromatics in the reaction network can be almost completely suppressed under suitable reaction conditions. By varying the reaction parameters temperature, DME partial pressure and weight hourly space velocity (WHSV), it was possible to identify the optimal combination of selectivity and deactivation resistance for each material. The olefin-rich DTH product of the *MRE zeolite offers manifold possibilities for further conversion to valuable renewably produced low-emission fuels like gasoline or jet fuel

Process Effluent Recycling in the Supercritical Water Gasification of Dry Biomass

The influence of process water recycling during the Supercritical Water Gasification (SCWG) of dry biomasses was investigated. Dry biomass has to be diluted with water to a dry matter content of approximately 10 wt.% to gasify it in the process of supercritical water gasification. The treatment of wastewater in the SCWG process is cost intensive due to organic contaminants; therefore, the recycling of the process effluent is attractive. Salt separation is needed to avoid accumulation of salts in the effluents, since salts enhance corrosion rates and might cause blocking of the flow when the effluent is recycled. The grass Reed Canary Grass and grapevines were gasified. The recycling of the process effluent did not influence the composition of the product gas. In both cases the carbon efficiency decreased by 4% when wastewater was used to dilute the biomass. An increase in organic carbon and potassium in the reactor effluent was observed after gasification of the biomass with recycled process effluent. The addition of potassium hydroxide to the feed as a homogenous catalyst needs to be closely monitored and adjusted according to the potassium content of the reactor effluent. Insufficient salt separation proved to be an issue regarding formation of solid deposits in the reaction system