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.

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.

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.

Failures of the High Energy, High Pitch Velocity Gear Boxes

This Paper describes the on-going efforts of finding the root-cause for the failures of high-energy (over 30,000 HP), high-pitch velocity (over 30,000 FPM) gear elements. These gear elements are presently operating in Oil and Gas Production Facilities. They are installed between the GT drivers and turbo-compressors. Turbo-compressors deliver high-pressure gas into the underground oil fields to enhance the oil production. The oldest Gas Compression Units were commissioned in 1995 and the latest in 1998. Since installation in 1995 at least 6 gear boxes experienced failures of the pinion (high speed gear) teeth. The Mean Time Between Failures (MTBF) of the pinion teeth was estimated around 34,000 operating hours. The costly shutdown of Gas Compression Units forced the management to seek advice within the company. The intent of this Paper is to share some field experiences and to present some corrective actions. The intent of this Paper is also to help Original Equipment Manufacturers (OEMs) in this case gear elements Manufacturers to develop better balance between cost, life and reliability. Sometimes the balance between these three parameters is difficult to maintain. Too often the gear elements Manufacturers are forced to compete on the price basis and as result the quality of the gear elements are sometimes compromised. In addition, several well-known gear elements Manufacturers stopped offering high energy, high-pitch velocity gear elements because they suffered serious failures of the gear elements on the test stand and also in the field.

The Ethanol-Water Humidification Process in EvGT Cycles

Ethanol from bio-products has become an important fuel for future power production. However, the present production technology is rather expensive. This paper focuses on how to lower the production cost of ethanol extraction from mash, and to use the ethanol as a primary fuel in gas turbines for heat and power production. Today, ethanol is produced during distillation by supplying energy to extract the ethanol from the mash. Using the evaporation process in the evaporative gas turbine to extract the ethanol from the mash before the distillation step, a lot of energy can be saved. In the evaporation process, the ethanol is extracted directly from the mash using energy from low-level energy sources. The evaporation technology is therefore expected to reduce the cost for the ethanol production. Simultaneous heat and mass transfer inside the ethanol humidification tower drives a mixture of ethanol and water into the compressor discharge air. To investigate the evaporation of a binary mixture into air at elevated pressures and temperatures, a test facility was constructed and integrated into the evaporative gas turbine pilot-plant. The concentration of ethanol in the mash is not constant but depends on the sugar content in the feedstock used in the fermentation process. Tests were therefore conducted at different concentrations of ethanol in the ethanol-water mixture. Tests were also performed at different temperature and flow conditions to establish the influence of these parameters on the lower heating value of the produced low calorific gas. It has been shown that this technology extracts about 80% of the ethanol from the mash. It has also been shown that the composition of the resulting gas depends on the temperatures, flow rates and composition of the incoming streams. The tests have shown that the produced gas has a lower heating value between of 1.8 to 3.8 MJ/kg. The produced gas with heating values in the upper range is possible to use as fuel in the gas turbine without any pilot flame. Initial models of the ethanol humidification process have been established and the initial test results have been used for validating developed models.

Regenerative Gas Turbines With Divided Expansion

Recuperated gas turbines are currently drawing an increased attention due to the recent commercialization of micro gas turbines with recuperation. This system may reach a high efficiency even for the small units of less than 100kW. In order to improve the economics of the plants, ways to improve their efficiency are always of interest. Recently, two independent studies have proposed recuperated gas turbines to be configured with the turbine expansion divided, in order to obtain higher efficiency. The idea is to operate the system with a gas generator and a power turbine, and use the gas from the gas generator part for recuperation ahead of the expansion in the power turbine. The present study is more complete than the predecessors in that the ranges of the parameters have been extended and the mathematical model is more realistic using an extensive simulation program. It is confirmed that the proposed divided expansion can be advantageous under certain circumstances. But, in order for todays micro gas turbines to be competitive, the thermodynamic efficiencies will have to be rather high. This requires that all component efficiencies including the recuperator effectiveness will have to be high. The advantages of the divided expansion manifest themselves over a rather limited range of the operating parameters, that lies outside the range required to make modern micro turbines economically competitive.