Pre-dried Lignite Research Articles

Fluidized bed gasification of solid recovered fuels in a 500 kWth pilot plant

On the way to climate-neutrality with low resource consumption, the economics worldwide needs ways to obtain high-quality products from existing material flows. If waste is used as a feedstock for gasification, high-quality syngas is obtained from which new products for the chemical industry (e.g. methanol) or the transport sector (Fischer-Tropsch products) can be obtained. The fluidized bed-based High-Temperature-Winkler process is particularly suitable for the gasification of solid recovered fuel (SRF) and biomass that are difficult to grind since the feedstock can be processed in lump form. The gasification characteristics of SRF pellets were investigated in a 500 kWth pilot gasifier at the Technical University of Darmstadt. After a co-gasification with pre-dried lignite, a mono SRF gasification could be realized. This paper presents the effects of operating temperature and the SRF content in the feedstock on the syngas quality, which is characterized by the target components CO and H2, the undesired fraction of CH4, and some representative higher hydrocarbons. It could be shown, that the syngas gas components CO and H2 depend mainly on the gasification temperature and not on the used feedstock. On the other hand, the higher amount of volatiles in the SRF fraction rises the methane concentration and the amount of higher hydrocarbons in the syngas. It was observed that these components are decomposed at higher gasification temperatures and an almost tar-free syngas is produced.

Pilot-Scale Experiences on a Plasma Ignition System for Pulverized Fuels

The need for flexible power generation is growing worldwide as the energy transition is altering the operational regimes of thermal power plants. Plasma ignition systems, as an alternative technology to the conventional start-up method with natural gas or oil firing, offer a cost- and energy-efficient start-up process in pulverized fuel power stations. The application of plasma ignition systems for cold start-ups using different qualities of pre-dried lignite is investigated in a pilot-scale combustion facility. A plasma integrated swirl burner is developed and validated using highly ignitable lignite dust. Eight pre-dried lignite qualities with a moisture content of up to 30% and a broad particle size distribution are investigated for this application to determine the applicability and limitations of the plasma ignition system with regard to the fuel quality. The performance of lignites for cold start-up in the plasma ignition system are categorized based on their ignition and combustion performance. All lignite qualities were ignited under the cold-start-up condition with a plasma power of 4 kW to 7 kW. Lignite qualities with a moisture content of up to 20% and a median particle size of below 450 μm form a self-sustained flame with short-time plasma-supported combustion, while flame blow-out is observed for lignites with lower qualities.

Nanoparticle Emission and Characterization from Pre-Dried Lignite and Bituminous Coal Co-Combustion

Nowadays, the high share of electricity production from renewables drives coal-fired power plants to adopt a more flexible operation scheme and, at the same time, maintain flue gas emissions within respective standards. A 500 kWth pulverized coal furnace was used to study pre-dried lignite combustion or co-combustion as an available option for these plants. Bituminous coal from Czech Republic and pre-dried lignite from Greece were blended for the experiments. Particle emissions measurements with a heated Electrical Low Pressure Impactor (ELPI+) and Scanning Electron Microscopy with Energy Dispersive Spectroscopy (SEM/EDS) analyses were performed. The effect of the pre-dried lignite proportions in the fuel feed and the combustion conditions regarding the combustion air staging were the two parameters selected for this study. Skeletal density values were measured from the cyclone prior to the impactor. Results are depicted with respect to the aerodynamic and Stokes diameter for impactor stages. The presence of pre-dried lignite in the fuel blend lowers the particle matter (PM) PM2.5, PM1 and PM0.1 emissions, thus having a positive impact on ESP’s fractional and overall efficiency. The staged combustion air feed reduces the particle emissions in all cases. Sulfur content follows a pattern of higher concentration values for finer particles.

Numerical comparative investigation of a flexible lignite-fired boiler using pre-dried lignite or biomass as supporting fuel

This work presents a numerical parametric investigation of an indirect firing scheme for a lignite-fired boiler during its operation at a thermal load of 35% of the nominal one, lower than the current technical minimum. The parametric investigation is important in order to evaluate different configurations of the firing concept and the impact of two different types of supporting fuels: pre-dried lignite and exhausted olive cake. Numerical results indicate that both types of supporting fuel can ensure the stable operation of the boiler at the reduced operating load. Moreover, it can be remarked, that the injection of biomass as supporting fuel improves the thermal efficiency of the boiler. Furthermore, the firing system setup especially for the injection of pre-dried lignite affects significantly the NOx emissions due to the developed temperature field. Finally, simulation results indicate that the injection of biomass particles through all vapour burners induces high thermal loading on boiler surfaces. Therefore, it is proved that the firing strategy plays a key role to the operation of a boiler using these fuel blends.

HTW™-gasification of high volatile bituminous coal in a 500 kWth pilot plant

Processing of difficult feedstock’s like high-ash coal or biogenic residues poses a challenge for most common gasification technologies. The High-Temperature-Winkler (HTW™) gasifier, as part of the fluidized bed gasification technologies might very well provide a solution for these feedstock’s. Gasification takes place in the two characteristic zones of the gasifier (bubbling fluidized bed zone and post gasification zone) enabling dry ash removal, while the majority of heavy hydrocarbons like tars are converted. A semi industrial HTW™ pilot plant was erected at the Institute for Energy Systems and Technology by retrofitting a circulating fluidized bed reactor in cooperation with thyssenkrupp Industrial Solutions AG (former ThyssenKrupp Uhde GmbH). Commissioning was successfully carried out in June 2015 using pre-dried lignite. This study shows the usability of the HTW™ technology for an increased variety of feedstocks, by means of high volatile bituminous coal (HVBC). Furthermore, significant workload was put into identification of optimizations for the pilot plant in order to increase performance, handling and quality of the gasification process. During the 5 days of continuous operation, 7.4 tons of HVBC were gasified to examine the gasifier behavior depending on the feedrate, temperature and distribution of gasification agents. During these tests syngas containing more than 50 vol% CO and H2 was produced. The syngas quality significantly increases with the temperature, while the gasifier load and the particle size showed mixed results. Increasing the load (feedrate) of the gasifier resulted in decreasing temperatures. More particles were entrained into and through the post gasification zone, reducing efficiency and carbon conversion rate as well as syngas quality.Optimizations of the gasifier include removal of the loop seal from the return leg, reducing the overall CO2 injection by at least 20%. Furthermore, an optimized cyclone was developed to significantly increase separation efficiency and carbon conversion rate. Increased temperature of the gasification agents will benefit the overall energy balance of the gasifier increasing performance and syngas quality and decreasing freeboard velocity. The temperature dependence of the gasification of HVBC indicate significant improvement in syngas quality for this feed by an increase of gasifier temperatures. The evaluation and verification of these optimizations will be done during the next longterm tests of the gasifier using pre-dried lignite.

Thermal Simulation and Economic Study of Predried Lignite Production Retrofit of a Greek Power Plant for Enhanced Flexibility

AbstractThe use of predried lignite as a factor to enhance flexibility of existing power plants is considered as a practically feasible step to ensure power supply and grid stability. In this work,...

Experimental investigations of oxyfuel burner for cement production application

The production of cement is one of the CO2 intensive processes, due to the inherent formation of CO2 in the calcination process by decomposition of limestone which is additional to the CO2 generated from fuel combustion. Carbon capture and storage technologies have been seen as a promising way to comply with CO2 reduction targets. As part of the objectives of the Horizon 2020 project CEMCAP, the retrofitting of key parts of the equipment of a conventional cement plant to oxyfuel combustion are investigated. The present study reports the results of several combustion tests employing a downscaled commercial kiln burner to determine its adequacy for oxyfuel operation mode. The investigations were carried out in the 500 kWth top-fired combustion facility at University of Stuttgart, which was previously adapted for these tests, including the installation of an electric preheating system to rise secondary gas temperature up to 800 °C. Fuel used is a German pre-dried lignite previously milled to required fineness in a separate location. A variety of in-flame measurements are performed at a dozen of ports located at different distances from burner outlet in order to characterize combustion behavior in each firing mode. It was observed that under oxyfuel mode additional parameters in burner configuration like total oxygen concentration and oxygen distribution in primary and secondary gas are key variables to adjust flame formation and obtain similar results as in conventional air firing.

Comparative investigation of a co-firing scheme in a lignite-fired boiler at very low thermal-load operation using either pre-dried lignite or biomass as supporting fuel

This work presents an investigation of an indirect firing scheme using biomass (cardoon) as supporting fuel for a pulverized-lignite boiler during its operation at a thermal load of 35%, lower than the current minimum one. Results are compared with an alternative indirect firing scheme which employs pre-dried lignite (PDL) as supporting fuel. The numerical investigation of the boiler has been conducted using the commercial software ANSYS Fluent® v15.0, supported by in-house built functions for the combustion rate of the fuels and the drag force exerted on biomass particles. The simulation and the comparison of the combustion of two different fuel blends in a co-firing strategy is important in order to evaluate technically the available possibilities and select among them the optimal firing concept (number and position of the operating injection ports) and the ideal fuel blend for the operation of the unit at lower than technical minimum thermal loads, in order to attain reduction of emissions and improvement of the boiler flexibility. Due to the implementation of a two-stage over-fire air (OFA) system and the consideration of sub-stoichiometric conditions exhibited at the nominal load, this work also takes into consideration the modeling of the boiler convective section, following the porous media analysis provided by the available Macro Heat Exchanger Model, ANSYS Fluent®. The validation of the applied models has been performed in previous works of the same group of authors, while the combustion results regarding crucial combustion parameters have been compared against corresponding values derived by a suitably-developed thermodynamic model. The agreement between these two models is good, since the maximum percentage deviation is calculated to be in the range of approximately 10%. Based on the numerical results, it can be concluded, that the utilization of both types of supporting fuel can ensure the stable operation of the boiler at thermal loads, lower than the technical minimum of the unit, promoting its flexibility. Between the two different supporting fuels, it is observed, that biomass ensures higher combustion efficiency compared to pre-dried lignite. However, it is also indicated, that the reduction of NOx emissions and the intensity of the induced thermal loading on the membrane walls with the utilization of biomass is more dependent on the firing strategy compared to lignite, proving the key role that this parameter plays to the operation of a boiler using this specific fuel blend.

The Impact of Predried Lignite Cofiring With Hard Coal in an Industrial Scale Pulverized Coal Fired Boiler

The paper presents the experimental and numerical study on the behavior and performance of an industrial scale boiler during combustion of pulverized bituminous coal with various shares of predried lignite. The experimental measurements were carried out on a boiler WP120 located in CHP, Opole, Poland. Tests on the boiler were performed during low load operation and the lignite share reached over to 36% by mass. The predried lignite, kept in dedicated separate bunkers, was mixed with bituminous coal just before the coal mills. Computational fluid dynamic (CFD) simulation of a cofiring scenario of lignite with hard coal was also performed. Site measurements have proven that cofiring of a predried lignite is not detrimental to the boiler in terms of its overall efficiency, when compared with a corresponding reference case, with 100% of hard coal. Experiments demonstrated an improvement in the grindability that can be achieved during co-milling of lignite and hard coal in the same mill, for both wet and dry lignite. Moreover, performed tests delivered empirical evidence of the potential of lignite to decrease NOx emissions during cofiring, for both wet and dry lignite. Results of efficiency calculations and temperature measurements in the combustion chamber confirmed the need to predry lignite before cofiring. Performed measurements of temperature distribution in the combustion chamber confirmed trend that could be seen in the results of CFD. CFD simulations were performed for predried lignite and demonstrated flow patterns in the combustion chamber of the boiler, which could prove useful in case of any further improvements in the firing system. CFD simulations reached satisfactory agreement with the site measurements in terms of the prediction of emissions.

A thermodynamic analysis and economic evaluation of an integrated lignite upgrading and power generation system

Effective upgrading for efficient utilisation of lignite is of great significance for countries that highly dependent on coal for power generation. This work proposed and evaluated an integrated system for lignite upgrading and utilisation using pre-drying, low-temperature oxidative pyrolysis (LTOP) and power generation, beneficially converting lignite into an exportable thermal coal while generating power locally. In the proposed system, LTOP was adopted to upgrade lignite, and the pre-drying process would reduce the moisture content of lignite prior to LTOP and boiler using steam bleeds from the conjunct steam turbine, saving a part of reaction heat consumed by moisture evaporation. The energy of raw syngas produced in LTOP process was efficiently utilised by co-combusting with a portion of pre-dried lignite in boiler, and the sensible heat of upgraded coal was recovered by preheating the feed/condensate water of steam turbine unit. With the developed models and process simulation, the mass and energy balance of the proposed integrated system for upgrading Zhundong lignite (ZD) in conjunction with a 600 MW supercritical electric power plant were determined. Detailed thermodynamic analysis showed that the proposed system produces annually 1.66 million tonnes of exportable upgraded coal with lower heating value (LHV) of 29.45 MJ/kg, as well as 3118.5 GWh electricity, with overall energy efficiency at 79.6% and the ratio of produced electricity over the energy of upgrade coal product at 22.9%. As a considerable technical route for long-distance energy transportation, economics of deploying the proposed systems in north-western China and exporting the upgraded coal (TR-I) to the eastern seaboard over a distance of 3000 km was quantified, and compared with the option of adopting ultra-high voltage (UHV) electric power transmission (TR-II). It was shown that, the overall CAPEX of TR-I is ∼59% less than that of TR-II and the gross cost of electricity (COE) of TR-I is ₵5.20/kWh, also much lower than that of the TR-II.

Combustion measurements of type-1 pulverized coal flames operating under oxy-fired conditions

The present study addresses the impact of oxy-fired conditions on type-1 flames generated by an oxidant-staged burner operating with pre-dried lignite and applying wet flue-gas recirculation. Investigations were carried out in a laboratory facility where the combustion takes place in a furnace with a rated capacity of 0.40MWth. In-flame measurements were performed for oxy-fired conditions operating at three levels of secondary swirl number (1.15, 1.65, and 2.05), while overall O2 fraction upstream of the burner in oxy-firing was kept at 31vol%. One air-fired condition at 1.65 secondary swirl number was also investigated. Measurements of local gas temperature and gas species concentrations were performed using standard water-cooled probes with focus on the near burner region. Results showed evidence of radial flame stratification consistent with gradual O2 admixing to the central fuel jet. Lower temperatures on the flame axis were obtained under oxy-fired condition. In the same region, as a result of CO2 dissociation and/or gasification reactions by water vapor and CO2, higher CO concentrations were also monitored, which contributed to lower temperatures. Experimental data also suggested great potential for NO abatement through flame stratification due to type-1 flame pattern.

Influence of critical moisture content in lignite dried by two methods on its physicochemical properties during oxidation at low temperature

Different drying methods resulted in the pore structure and free radical distribution changing in lignite, and significantly influences its chemical properties and potential utilizations. In this study, the influence of moisture content on characteristic temperature of lignite dried in N2 and air were explored in a simulating coal oxidation device. Electron Spin Resonance (ESR) and carbon-13 nuclear magnetic resonance (13C NMR) were applied to investigate the free radical parameters and the functional groups concentrations in dried lignite. The initial oxidation of lignite occurs at above separation point temperature (SPT), and make pre-dried lignite achieve self-heating. Compared to vacuum drying, the lignite dried in N2 with critical moisture content of about 15% release more heat during oxidation. Focus was directed on comparisons of free radical characteristics of lignite dried in N2 at different oxidation temperature, indicating that dried lignite with higher oxidation temperature have a greater free radical concentration and line-width. Mesopore formed by the shrinkage of macropore in lignite dried in N2 occurred further shrinkage and collapse to form more micropore. When the coal seam temperature reached 140°C and close to SPT, the yields of gas products such as CO2 and CO increase rapidly. The values of oxygen-containing functional group measured in FTIR and 13C NMR spectra show that the distinct structural feature of lignite dried in vacuum is larger than that of in N2 due to the greater drying intensity.

Predictive method for low load off-design operation of a lignite fired power plant

The increasing share of renewable energy sources and their stochastic attitude of power production force the conventional fossil fuel thermal plants to operate in a more flexible mode, with rapid load changes (ramp up/down rates) and in lower thermal loads than their current technical minimum. This can be achieved with the use of pre-dried lignite as a supporting fuel, in the place of conventional liquid fuels such as diesel. This study presents a thermodynamic methodology for the prediction of Agios Dimitrios V Greek lignite fired boiler at low power loads; even below the current technical minimum, when pre-dried lignite is employed. The calculations are based on measurement data provided for the current operating thermal loads of 100%, 80% and 60% (current technical minimum). Among the controlling values of critical operational parameters, this model takes into account the thermodynamic properties (pressure, temperature and steam quality) of SH and RH steam, the steam turbine properties, the heat transfer coefficient of the heat exchangers and the fuel combustion specifications. The model of the boiler is developed in Aspen Plus whereas the ST model was built in GateCycle. Furthermore, this house-built model is implemented to estimate the heat transfer coefficients for the theoretical scenario of 35% thermal load operation, which is far below the current technical minimum and no design or measurement data exist for them. Thermodynamic calculations reveal the boiler effective operation of the boiler even at a thermal load of 35% with a quite good overall thermal efficiency. The net efficiency of the theoretical new technical minimum load is 0.9 percentage points higher than the current one. Results of this approach are also compared against corresponding CFD results, with a fairly good accordance.

Numerical examination of an operationally flexible lignite-fired boiler including its convective section using as supporting fuel pre-dried lignite

This work simulates the main furnace and the convective section of the lignite-fired Ag. Dimitrios V boiler located in Kozani, Northern Greece, under three different thermal loads (100%, 60% and 35% of the nominal one) using the Ansys Fluent 15.0® software program. The lowest thermal load investigated, i.e. 35% of the nominal one, is lower than the current technical minimum of the unit (~55%). In order to ensure the furnace stability and efficiency in this low thermal load, a co-combustion scheme of pre-dried with raw lignite is implemented. Due to sub-stoichiometric operating conditions in the main furnace zone in the full-load case and the formation of a two-stage over-fire air (OFA) system, the simulation of whole the furnace, including both the main furnace and the convective section of the boiler, is necessary, to investigate the char conversion and the furnace performance thoroughly. The simulation of the convective section is based on the porous media analysis using the Macro Heat Exchanger Model provided by Ansys Fluent 15.0®. The results regarding the total heat transfer towards the working medium and the flue gas average temperature at the main furnace outlet surface and at characteristic transversal surfaces of the convective section are compared against thermodynamic model predictions and experimental values showing good agreement, since the maximum percentage difference between the results of the two software tools and with the experimental values is approximately equal to 10%. Based on these results, it is indicated that the injection of pre-dried lignite fuel ensures the combustion stability and high efficiency of the boiler in lower thermal load (35%) than the current technical minimum of the unit.

Experimental investigations in a demonstration plant for fluidized bed gasification of multiple feedstock’s in 0.5 MWth scale

The High-Temperature Winkler process (HTWTM), which has been developed by the companies Rheinbraun and Uhde in the mid-70s of the 20th century, is an evolution of the Winkler-fluidized bed gasification process. The gasifier is divided into two zones, the bubbling fluidized bed operated at temperatures well below the ash softening point, and the freeboard operated at higher temperatures in order to decompose tars contained in the produced gas. The obtained gas may be used either in a gas turbine for power generation or for the production of fuels or chemical products. At the Institute for Energy Systems and Technology (EST) of TU Darmstadt, a semi-industrial pilot plant with thermal capacity of 0.5MWth has been erected to test the HTWTM gasification technology for different kinds of feedstock. A fluidized bed reactor with an inner diameter of 0.4m is used as gasifier. Gasification of the feedstock’s is carried out under atmospheric pressure. The cold and the hot commissioning of the plant have successfully been conducted. This paper presents first results and experiences gained within the commissioning of the pilot plant using pre-dried lignite as feedstock.

Lignite drying with solar energy: Thermodynamic analysis and case study

ABSTRACTAs a clean, free, and nondepleting source, solar energy has become the focus of increasing attention in the drying industry. A lignite-fired power plant integrated with a solar dryer (LPPS), in which solar energy is used to dry lignite and the predried lignite is used to generate electricity, is analyzed theoretically in this paper. The aim of this study is to evaluate the energy performance of solar drying under different system parameters. Thermodynamic models, with which the second-law efficiency of the LPPS could be maximized, were developed. A reference case with three kinds of lignite as input fuel was analyzed to quantify the system performance. The first-law and second-law efficiencies were obtained. The solar-to-electric conversion efficiency in the LPPS is more than 34%. Therefore, solar drying is a potential technology that should be promoted in lignite-deposited areas. Moreover, the influence of main parameters on the performance of system was analyzed. Dryer efficiency is determined to have significant influence on the solar-to-electric conversion efficiency.

Pre-dried lignite technology implementation in partial load/low demand cases for flexibility enhancement

The contribution of Renewable Energy Sources to the electricity production is gradually increasing, and due to the stochastic fluctuations of their load curve, the necessity for flexible operation in the fossil fuel power plants is boosted. The present study examines various scenarios of lignite drying and utilization depending on power load variation of the plant during certain periods of the day, in order to simultaneously increase the plant efficiency and reduce the electricity cost. The main goal is to evaluate the economic feasibility of the concepts, the reduction in the cost of electricity and the CO2 emissions avoidance. The thermodynamic analysis of a lignite power plant includes the mass and energy balance calculations at full and partial loads using either raw or raw/dried lignite mixture. The operation of the drying system in periods when the plant operates in partial load turned out to be the most suitable mode. Economic analysis revealed that employing the proposed scenario, the increase in the income from electricity can be more than 3.5–4.0%. The annual CO2 emissions savings can reach 130,000tn. The dryer cost, the fuel price and the CO2 emissions allowances affect significantly the profit from the electricity sales.

Numerical investigation of firing concepts for a flexible Greek lignite-fired power plant

In the present work the behavior of a lignite boiler under both full and partial load conditions is investigated by means of CFD modeling. The simulated furnace is that of the Megalopolis Unit IV, a 300MWe power plant operated by Public Power Corporation S.A. (PPC) and located in Peloponnese, Southern Greece. Due to the extremely low quality lignite utilized in the particular power plant, a special system for dried lignite dust separation from vapors — composing of a) an additional vapor ESPs – partial vapor discharge and b) a dry lignite dust recirculation and firing system, is designed and operated in the particular boiler. Hence, pre-dried lignite is continuously used as the additional supporting fuel, through a special feeding, dosing and firing system along with separation and vapor discharge.Scope of the present work is the evaluation and optimization of different firing modes for the decrease of minimum load operation lower than 40%. The numerical analysis is focused on the induced flue gas flow field characteristics, associated with average exhibited temperature, main gas species concentrations, wall heat flux and particle burnout. The boundary conditions for partial load operation are provided by Mitsubishi Hitachi Power Systems Europe (MHPSE) and the basic design data of the furnace are provided by PPC S.A. In total, eight operating conditions are investigated corresponding to five boiler thermal loads, thus covering a wide range of thermal load operation. Furthermore, the boiler performance under different air and fuel distributions among the burners is also examined, in order to identify useful trends regarding the optimum conditions, under which a stable and safe furnace operation for very low load operation (less than 40%) can be assured. The CFD results are compared against design values provided by MHPSE. Finally, conclusions concerning the furnace membrane wall erosion and accretion rates under various operating configurations are derived, providing useful information about potential operating issues that could be expected, if the examined firing cases were applied. Finally, the case of a thermal load equal to 40% is of interest, for which a stable pulverized lignite flame can be achieved when two mills instead of three are operating.

Simulation study on lignite-fired power system integrated with flue gas drying and waste heat recovery – Performances under variable power loads coupled with off-design parameters

Lignite is a kind of low rank coal with high moisture content and low net heating value, which is mainly used for electric power generation. However, the thermal efficiency of power plants firing lignite directly is very low. Pre-drying is a proactive option, dehydrating raw lignite to raise its heating value, to improve the power plant thermal efficiency. A pre-dried lignite-fired power system integrated with boiler flue gas drying and waste heat recovery was proposed in this paper. The plant thermal efficiency could be improved by 1.51% at benchmark condition due to pre-drying and waste heat recovery. The main system performances under variable power loads were simulated and analyzed. Simulation results show that the improvement of plant thermal efficiency reduced to 1.36% at 50% full load. Moreover, the influences of drying system off-design parameters were simulated coupled with power loads. The variation tendencies of main system parameters were obtained. The influence of pre-drying degree (including moisture content of pre-dried lignite and raw lignite) on the plant thermal efficiency diminishes gradually with the decreasing power load. The dryer thermal efficiency and dryer exhaust temperature are also main factors and the influences on system parameters have been quantitatively analyzed.

Pyrolysis of Hailar lignite in an autogenerated steam agent

An in situ pyrolysis process of high moisture content lignite in an autogenerated steam agent was proposed. The aim is to utilize steam autogenerated from lignite moisture as a reactant to produce fuel gas and additional hydrogen. Thermogravimetric analysis revealed that mass loss and maximum mass loss rate increased with the rise of heating rates. The in situ pyrolysis process was performed in a screw kiln reactor to investigate the effects of moisture content and reactor temperature on product yields, gas compositions, and pyrolysis performance. The results demonstrated that inherent moisture in lignite had a significant influence on the product yield. The pyrolysis of L R (raw lignite with a moisture content of 36.9 %, wet basis) at 900 °C exhibited higher dry yield of 33.67 mL g−1 and H2 content of 50.3 vol% than those from the pyrolysis of the predried lignite. It was also shown that increasing reaction temperature led to a rising dry gas yield and H2 yield. The pyrolysis of L R showed the maximum dry yield of 33.7 mL g−1 and H2 content of 53.2 vol% at 1,000 °C. The LHV of fuel gas ranged from 18.45 to 14.38 MJ Nm−3 when the reactor temperature increased from 600 to 1,000 °C.