Special Issue "Thermochemical Conversion Processes for Solid Fuels and Renewable Energies"

The world society ratifies international measures to reach a flexible and low-carbon energy economy, attenuating climate change and its devastating environmental consequences. The main contribution of this Special Issue is related to thermochemical conversion technologies of solid fuels (e.g., biomass, refuse-derived fuel, and sewage sludge), in particular via combustion and gasification. Here, the recent activities on operational flexibility of co-combustion of biomass and lignite, carbon capture methods, solar-driven air-conditioning systems, integrated solar combined cycle power plants, and advanced gasification systems, such as the sorption-enhanced gasification and the chemical looping gasification, are shown

Design of a 1 MWth Pilot Plant for Chemical Looping Gasification of Biogenic Residues

Chemical looping gasification (CLG) is a promising process for the thermochemical solid to liquid conversion route using lattice oxygen, provided by a solid oxygen carrier material, to produce a nitrogen free synthesis gas. Recent advances in lab-scale experiments show that CLG with biomass has the possibility to produce a carbon neutral synthesis gas. However, all experiments have been conducted in externally heated units, not enabling autothermal operation. In this study, the modification of an existing pilot plant for demonstrating autothermal operation of CLG is described. Energy and mass balances are calculated using a validated chemical looping combustion process model extended for biomass gasification. Based on six operational cases, adaptations of the pilot plant are designed and changes discussed. A reactor configuration using two circulating fluidized bed reactors with internal solid circulation in the air reactor is proposed and a suitable operating strategy devised. The resulting experimental unit enables a reasonable range of operational parameters within restrictions imposed from autothermal operation

Acceleration of Load Changes by Controlling the Operating Parameters in CFB Co-Combustion

The integration of intermittent renewable energy sources into the electricity market requires flexible and efficient technologies that compensate for the fluctuating electricity demand. A circulating fluidized bed (CFB) boiler is a suitable solution due to its fuel flexibility, but the thermal inertia of the fluidized bed can have negative effects on the load following capabilities. This study investigates the influence of the operating parameters of the fire side on the speed of load changes on the waterside. Co-combustion of lignite, straw, and refuse derived fuel (RDF) was carried out. In a 1 MWth pilot CFB combustor fifteen load changes were performed with a varying step input of the primary air, the secondary air, and the fuel mass flow. The step input of the primary air had a large influence on the load ramps, as it strongly affects the solids concentration in the upper furnace. The step size of the fuel mass flow had a positive effect on the load change rate. Based on the results, concepts were developed to accelerate load ramping by controlling the hydrodynamic conditions and the temperature on the fireside

Adaption of a 300 kWth Pilot Plant for Testing the Indirectly Heated Carbonate Looping Process for CO2 Capture from Lime and Cement Industry

The indirectly heated carbonate looping process (IHCaL) is a promising technology for decarbonizing one major emitter of CO2, the lime and cement industry. Another advantage of the IHCaL is the synergy with these industries using same solid materials. Recent pilot tests showed the feasibility of the IHCaL for applications in the power plant sector, bringing the technology to a readiness level (TRL) of five. However, the integration of the IHCaL into cement and lime plants, as well as the usability of spent sorbents as educts in such productions, has not yet been proven in industrially relevant conditions. In this study, the modification of an existing 300 kWth pilot plant for demonstrating the IHCaL process in industrially relevant conditions for cement and lime is described. Energy and mass balances are calculated. On the basis of operational cases, adaptations of the pilot plant are designed, and modifications are discussed. A reactor configuration with multiple interconnections between the reactors are assessed and operational parameters are defined. The resulting experimental setup enables a wide range of variation of the operational parameters for the pilot testing

Efficient CO2 Capture from Lime Plants: Techno-economic Assessment of Integrated Concepts using Indirectly Heated Carbonate Looping Technology

The quest to decarbonize the lime and cement industry is challenging because of the amount and the nature of the CO2 emissions. The process emissions from calcination are unavoidable unless carbon capture is deployed. Nevertheless, the majority of the available carbon capture technologies are expensive and energy inefficient. The indirectly heated carbonate looping (IHCaL) process is a promising technology to capture CO2 from the lime and cement production, featuring low penalties in terms of economics and energy utilization. Previous works have highlighted the potential of the IHCaL, but the optimization of the process has not been discussed in enough detail and techno-economic implications are not yet fully understood. Within this work, ten scenarios using IHCaL technology to capture CO2 from a lime plant were simulated. Hereby, different process configurations, heat recovery strategies and fueling options were computed. The calculations for the capture facilities were performed with Aspen Plus® software and EBSILON®Professional was used to simulate the steam cycles. A techno-economic assessment was included as well, aided by the ECLIPSE software. The results demonstrate that the selection of the fuel for the combustor not only affects the CO2 balance and energy performance but is also an important cost driver —there were considerable economic advantages for the computed cases with middle-caloric solid recovered fuel (SRF). The analysis shows how the heat recovery strategy can be optimized to achieve tailored outcomes, such as reduced fuel requirement or increased power production. The specific primary energy consumption (from –0.3 to +2.5 MJLHV/tCO2,av) and cost for CO2 avoided (from –11 to +25 €/tCO2,av) using SRF are considerably low, compared with other technologies for the same application. The sensitivity study revealed that the main parameters that impact the economics are the discount rate and the project life. The capture plants are more sensitive to parameter changes than the reference plant, and the plants using SRF are more sensitive than the lignite-fueled plants. The conclusions from this work open a new pathway of experimental research to validate key assumptions and enable the industrial deployment of IHCaL technology before 2030

Diet-dependent net endogenous acid load of vegan diets in relation to food groups and bone health-related nutrients: Results from the German Vegan Study

Background/Aims:Dietary composition has been shown to affect acid-base homeostasis and bone health in humans. We investigated the potential renal acid load (PRAL) and the estimated diet-dependent net acid load (net endogenous acid production, NEAP) in adult vegans and evaluated the relationships between NEAP, food groups and intake of bone health-related nutrients. Methods: The German Vegan Study (GVS) is a cross-sectional study. Data from healthy men (n = 67) and women (n = 87), aged 21–75 years, who fulfilled the study criteria (vegan diet for ≧1 year prior to study start; age ≧18 years, and no pregnancy/childbirth during the last 12 months) were included in the analysis. NEAP values were calculated from diet composition using two models: one based on the protein/potassium quotient and another taking into account an anthropometry-based loss of urinary organic anions. Results:Mean daily intakes of phosphorus, potassium, sodium, magnesium and vitamin C were above, and vitamin D and calcium below Dietary Reference Intake (DRI). Regardless of the model used, the diet in the GVS was characterized by a nearly neutral NEAP. A strong correlation was observed between the NEAP values of the two models (rs = 0.873, p < 0.001). Only the consumption of fruits decreased constantly across the increasing quartiles of NEAP. Conclusions: It can be hypothesized that vegan diets do not affect acid-base homeostasis. With respect to bone health, the significance of this finding needs further investigation

Overall glycemic index and glycemic load of vegan diets in relation to plasma lipoproteins and triacylglycerols

Background: To investigate the overall glycemic index (GI), glycemic load (GL), and intake of dietary fiber, and to examine the associations between these factors and plasma lipoproteins and triacylglycerols in adult vegans in the German Vegan Study (GVS). Methods: Cross-sectional study, Germany. Healthy men (n = 67) and women (n = 87), who fulfilled the study criteria (vegan diet for ≧1 year prior to study start; minimum age of 18 years; no pregnancy/childbirth during the last 12 months) and who participated in all study segments. Results: The average dietary GL of the GVS population was 144, and the average GI was 51.4. The adjusted geometric mean total, HDL, and LDL cholesterol concentrations decreased across the increasing quartiles of GL, carbohydrate and dietary fiber intake. The associations between total cholesterol, HDL cholesterol, LDL cholesterol and GL density and GI were inconsistent. Also, associations between GI, GL, the intake of carbohydrates, and triacylglycerol concentration were not observed. Conclusions: Fiber-rich vegan diets are characterized by a low GI and a low to moderate GL. The data do not support the hypothesis that a carbohydrate-rich diet per se is associated with unfavorable effects on triaclyglycerols that would be predicted to increase the risk of coronary heart disease

Pilot testing of the indirectly heated carbonate looping process for lime plants

A major challenge in limiting the greenhouse gas emissions is the decarbonisation of energy intensive industries, where CO2 emissions are inevitable due to the production process, such as the production of lime. Depending on the type of kiln, one ton of burnt lime accounts for more than one ton of CO2. A variety of technologies to capture these emissions is available or currently being developed. The carbonate looping process (CaL) is one of the most promising capture technology in this sector, since it i) can be retrofitted to existing plants, ii) has a considerably low energy penalty, and iii) uses the same materials as the production process. It is a post-combustion CO2 capture technology using natural limestone as sorbent. In the carbonator, the CO2 in the flue gas stream is absorbed by calcium oxide (CaO), according the reversible carbonation reaction at a temperature of approximately 650°C. The formed calcium carbonate (CaCO3) is transferred to the calciner to be regenerated at a temperature of approximately 900°C. The required heat can be supplied either straight-forward via oxy-combustion in the calciner or indirectly, e.g. with heat pipes from an external combustor. The latter has advantage that no technically pure oxygen, which requires an energy intensive air separation unit (ASU), is necessary. This further improves the efficiency and economics of the process. The general feasibility of the indirectly heated carbonate looping process (IHCaL) has previously been demonstrated at pilot scale. Recently, the existing 300 kWth IHCaL pilot plant at Technical University Darmstadt has been modified and operated for over 400 hours, with the objective to investigate the feasibility of this technology to be integrated into lime plants. During the test period, three different fuels, i.e i) propane, ii) lignite, and iii) waste derived fuels, were fired in the combustor, and the CO2 contained in the associated flue gases was captured in the carbonator. A natural limestone from Germany with two different particle sizes was used as sorbent. Aiming at specific conditions comparable to an integration into a lime plant, CO2 was added to the flue gas stream and a high make-up rate replacing deactivated material was applied. A special focus was given on the generation of highly calcined material, which was purged from the system. The collected purge was analyzed in order to assess its chemical composition and usability as educt for lime production. During the 9th High Temperature Solid Looping Cycles Network Meeting comprehensive findings obtained during the pilot testing will be presented, such as i) the effect of variation in CO2 inlet concentration of the carbonator and make-up ratio on the process performance ii) performance of the heat pipe heat exchanger while firing different fuels, and iii) physico-chemical properties of the purged material

Untersuchung der Flammenstabilität und thermischen Strahlung in einer 1-MWth-Brennkammer unter Oxyfuel-Bedingungen

Um Skalierungseffekte einer Oxyfuel-Staubfeuerung im halbindustriellen Maßstab zu untersuchen, wird ein 1 MWth Oxyfuel-Brennkammersystem, basierend auf der Geometrie bzw. den aerodynamischen Eigenschaften der kleinskaligen Brenner im 40 kWth – 60 kWth Bereich, mit Hilfe von CFD ausgelegt und anschließend konstruiert und verbaut. Als Basis für die Modellierung des neuen Brenners wird ein CFD-Modell verwendet, das anhand eines 40 kWth Brenners validiert wurde. Beide Brenner weisen eine innere Rezirkulation auf, die wichtig für die Stabilisierung der Flamme ist. Im Wandbereich unterscheiden sich die Strömungsfelder deutlich, da es sich bei der halbindustriellen Brennkammer um eine Retrofit-Anlage handelt, die im Vergleich zu der kleineren Brennkammer nicht über eine Wandspülung verfügt. Mit dem hochskalierten Brenner sollen zukünftig Experimente bzgl. der Flammenstabilität durch Variation der Sauerstoffkonzentration, Drallzahl und Brennstoffe durchgeführt werden. Dabei kommen verschiedene optische Messverfahren, sowie ein Ellipsoidal Radiometer zum Einsatz um Spezies-, Geschwindigkeits-, Temperaturfelder, sowie die thermische Strahlung zu messen