Operation of a Circulating Fluidised Bed Biomass Gasifier

Energy generation from the use of biomass is gaining an increasing attention. Gasification of biomass at present, is widely accepted as a popular technical route to produce fuel gas for the application in boilers, engine, gas/micro turbine or fuel cell. Up to now, most of researchers have focused their attentions only on fixed-bed gasification and fluidised bed gasification under air-blown conditions. In that case, the producer gas is contaminated by high tar contents and particles which could lead to the corrosion and wear of blades of turbine. Furthermore, both the technologies, particularly fixed bed gasification, are not flexible for using multiple biomass-fuel types and also not feasible economically and environmentally for large scale application up to 10∼50 MWth. An innovative circulating fluidised bed concept has been considered in our laboratory for biomass gasification thereby overcoming these challenges. The concept combines and integrates partial oxidation, fast pyrolysis (with an instantaneous drying), gasification, and tar cracking, as well as a shift reaction, with the purpose of producing a high quality of gas, in terms of low tar level and particulates carried out in the producer gas, and overall emissions reduction associated with the combustion of producer gas. This paper describes our innovative concept and presents some experimental results. The results indicate that the gas yield can be above 1.80Nm3/kg with the calorific value of 4.5–5.0MJ/Nm3, and the fluctuation of the gas yield during the period of operation is 3.3%–3.5% for the temperature of 750–800 °C. In genera, the results achieved support our concept as a promising alternative for the gasifier coupled with micro/gas turbine to generate electricity.

Production of Hydrogen-Rich Gas Through Pyrolysis of Biomass in a Two-Stage Reactor

Biomass is quite abundant in the world, particularly in some countries like China. China has large quantities of straw and/or stalk-origin biomass resources and the attention is currently being paid to the exploitation of these resources to produce energy products via different technical solutions, among of which pyrolysis of biomass to produce hydrogen-rich gas is very promising as hydrogen is a very clear energy carrier. In this work, pyrolysis of rice straw, corn stalk and sawdust was carried out in a two-stage reactor (the first-stage reactor is a conventional fixed-bed pyrolyser, and the second-stage reactor is a catalytic fixed bed) to produce hydrogen-rich gas. The effect of catalytic bed on the pyrolysis behaviour have been investigated, with the emphasis on final product particularly hydrogen. The operation of the catalytic reactor appears significant in promoting biomass pyrolysis towards the production of gaseous products, especially hydrogen. At 750°C of the pyrolyser with rice straw as fuel, the use of the catalytic bed leads to the increases of gas yield from 0.41 Nm3/kg to 0.50 Nm3/kg, approximately 22% increase, and of H2 concentration from 33.79% to 50.80% in volume, approximately 50.3% increase, respectively. Compared with calcined dolomite, fresh nickel-based catalyst shows stronger catalytic effect on the pyrolysis of rice straw as its use in the catalytic bed results in the increase of gas yield from 0.41 Nm3/kg to 0.56 Nm3/kg, approximately 36.6% increase, and the increase of H2 concentration from 33.79% to 59.55% in volume, approximately 76.2% increase. Furthermore, two catalysts follow the same trend for the pyrolysis of corn stalk and sawdust. At temperature of 815°C, catalysts also follow the same trend. Catalytic bed can significantly reduce the level of tar which is carried out with the producer gas, to less than 1% of original level. Catalyst load or gas space velocity (hourly) has the influence on the gas yield and H2 concentration. 30% of load, i.e. gas space velocity (hourly) 0.9 × 104 h−1, appears reasonable. Beyond that, gas yield and H2 concentration remain almost unchanged.

Development of Coal Partial Gasification and Combustion System

A new system using combined coal gasification and combustion has been developed for clean and high efficient utilization of coal. Following are the processes. The coal is first partially gasified and the produced fuel gas is then used for industrial purpose or as a fuel for a gas turbine. The char residue from the gasifier is burned in a circulating fluidized bed combustor to generate steam for power generation. For having the experimental investigation, a 1MW pilot plant test facility has been erected. Experiments on coal partial gasification with air, and recycle gas have been made on the 1 MW pilot plant test facility. The results show that, with air as gasification agent, the system can produce 4–5MJ/Nm3 low heating value dry gas and fuel conversion efficiency attains 50–70% in the gasifier, and residue 20–40% converted in the combustor and total conversion efficiency in the system is over 90%. In the gasifier, the carbon conversion efficiency increases with the bed temperature and the air blown temperature. CaCO3 has an effective effect for sulfur removal in the gasifier. The sulfur removal efficiency attains 85% with Ca/S molar ratio 2.5. The system can produce 12–14MJ/Nm3 middle heating value day gas by using high temperature circulation solid as heat carrier and recycle gas or steam as gasification media, but the fuel conversion efficiency only attain 30–40% in the gasifier and most of fuel energy is converted in the combustor. CaCO3 has an obvious effect on tar cracking and H2S removal. The sulfur removal efficiency attains 80% with Ca/S molar ratio 2.5.

Practical Implications of Integrating Turbomachinery Into the Air Turborocket

The development of new reusable space launch vehicle concepts has lead to the need for more advanced engine cycles. Many two-stage vehicle concepts rely on advanced gas turbine engines that can propel the first stage of the launch vehicle from a runway up to Mach 5 or faster. One prospective engine for these vehicles is the Air Turborocket (ATR). The ATR is an innovative aircraft engine flowpath that is intended to extend the operating range of a conventional gas turbine engine. This is done by moving the turbine out of the core engine flow, alleviating the traditional limit on the turbine inlet temperature. This paper presents the analysis of an ATR engine for a reusable space launch vehicle and some of the practical problems that will be encountered in the development of this engine.

Vent Gas Collection From Gas Compressor Dry Gas Seals

Gasum is an importer of natural gas and is operating and maintaining the Finnish transmission pipeline in which the pressure is maintained with three compressor stations. Gasum’s compressor stations are unmanned and remotely controlled from the central control room. Some of the compressor units are equipped with dry gas seals. The otherwise satisfactory operation of dry gas seals has the disadvantage of methane emissions. Reduction of methane emissions has been stated as a target by international auspices of the Kyoto Protocol or through national programs seeking to reduce emissions. The application described in this paper to collect vent gases from the dry gas seals was installed into four of the compressor units during 2001. The compressors are centrifugal compressors: two of them are Nuovo Pignone PCL603 with PGT10DLE (10 MW) gas turbine and two are Demag DeLaval 2B-18/18 with Siemens Tornado gas turbines (6,5 MW). It is normal for dry gas seals to have a small leakage of gas through the seals due to the function principle and required cooling of the seals. This gas emitted from the seals is normally about of 5...10nm3/h per one compressor unit during operation and during the stand-still the leakage is almost zero. In the year 2000 the total amount of emitted gas in Gasum’s units was about 50.000 nm3 per four compressor units. The target was to find an efficient method to collect the dry gas seal vent gas and utilize it. The solution must be simple and its investment costs must be feasible. Injection of the vent gases to the gas turbine inlet air flow was selected as a solution among some alternatives. The operating experience so far has been several thousands of operating hours without any malfunctions. The amount of collected gas by this system has been in the range of 80.000 nm3 per annum. The total cost of the system for four compressor units was about 85.000€. The intention of this paper is not to describe any scientific approach to the issue but to present a practical solution with operating experience.

Measured Data Correction for Improved Fouling and Degradation Analysis of Offshore Gas Turbines

The authors suggest a straightforward methodology to correct measurement data in order to facilitate condition assessment of gas turbines. After data being prepared as such, a considerable improvement in accuracy is obtained in regard to condition evaluation of the machine. Such methodology brings proven benefits when regarding the fouling problem as well as washing scheduling at sites where the fouling process is relatively slow, e.g. offshore applications. Analyses of other relatively slow performance loss processes, like degradation, are also targeted. The usefulness of the methodology is validated against field data by employing advanced software tools and reliability and availability as well as condition and lifing prediction.

Evaluation of Topping and Bottoming Cycle Hybrid Power Plants With MCFC-Micro Turbine

The increasing use of electronic appliance has put a strain on the existing electrical supply system. The growing trend of distributed generation could result in small turbo generators being used in the home or rural area. Because small turbo-generator is ideally suited for coupling with a Molten Carbonate Fuel Cell (MCFC) stack, a high efficiency and flexible hybrid system representing a new total energy concept for the distributed power market is presented. This paper presents hybrid concept of bottoming and topping cycle MCFC-micro turbine system. The simulation models for micro turbine, MCFC stack and hybrid system are established. Based on an existing 10kW MCFC stack, we carried out the simulation on hybrid system. The results of the simulation are presented and discussed with particular regards to the selection of design point of different configurations of Hybrid System and design point performance of topping cycle and bottoming cycle Hybrid System.

Coupling of Biomass Steam Gasification and an SOFC-Gas Turbine Hybrid System for Highly Efficient Electricity Generation

An energetic model of an internal reforming solid oxide fuel cell (IRSOFC) is developed. It is integrated in a process coupling fluidized bed steam gasification of biomass and an IRSOFC-gas turbine hybrid cycle. Process simulation is performed using the software package IPSEpro. The model of the gasification and gas conditioning section is based on data from the 8 MW (fuel power) plant in Guessing/Austria, while the fuel cell is modeled based on recent literature data. Heat utilization for power generation is considered covering both hybrid cycle exhaust and heat from the gasification process. Electric efficiencies up to 43% are expected for combined heat and power application even at small plant capacities in the range of 8 MW fuel power.

Heat Recovery Steam Generator Design for a Graz Cycle Prototype Power Plant for CO2 Capture

The introduction of closed cycle gas turbines with their capability of retaining combustion generated CO2 can offer a valuable contribution to the Kyoto goal and to future power generation. Therefore, research and development at Graz University of Technology has lead to the GRAZ CYCLE, a zero emission power cycle of highest efficiency. The GRAZ CYCLE is still on a theoretical level, first tests with the turbo-machinery equipment were performed. In the GRAZ CYCLE fossil fuels are burned with pure oxygen which enables a cost-effective separation of the combustion generated CO2 by condensation. Cycle efficiencies as high as 63% can be reached. Taking the efforts for the oxygen supply into account the efficiency is reduced to 55% [1]. This work presents a further step towards a GRAZ CYCLE prototype plant, with special emphasis on the layout and design of the heat recovery steam generator (HRSG). The hot exhaust gas of the turbine consists mainly of CO2 and H2O. This exhaust gas causes higher demands on the HRSG. A faster corrosion of the heat exchangers and the recirculation of the cycle fluid have to be considered. Based on the design of conventional HRSGs, the necessary adaptations are discussed and economically evaluated.

Compressor Transient Behaviour

An important issue related to compressor and driver integration is the behaviour during driver trip. Field tests at Troll Kollsnes gas treatment plant have shown that under a short power outage and within certain operating scenarios, the compressor enters the surge- and rotating stall area. These problems lead to a reduced flexibility in the operation of the pipeline compressors. The 40 MW variable speed electric motor driven compressors have therefore been subjected to dynamic simulation analyses to reveal the transient response. Dynamic simulations based on earlier trip tests have been performed so as to understand what parameters affect the severity and duration of a surge under power outage. An elaborate plant model has been created with the dynamic simulation tool OTISS™ by AspenTech and tuned to represent the plant. The model is validated against actual plant tests and operating data. The paper reports experience from analyses of the compressor and driver behaviour during run down. It is based on earlier tests and dynamic simulations performed for the Troll Kollsnes gas treatment plant. The main objective has been to study the compressor system sensitivity related to variation in polar inertia, driver power decay and trip signal delay on the transient rundown behaviour.