610 Choice Of Oxidant

All gasification processes require an oxidant for the partial oxidation reaction. There are essentially two alternatives air, which is available in unlimited quantities at the location of the gasifier and oxygen, which has to be separated from the nitrogen in the air at considerable cost. A third alternative, oxygen-enriched air, is essentially a mixture of the two. Historically, the first continuous partial oxidation systems, producer gas generators, operated with air. The idea of operating...

Info

TO AND FROM -* SOOT SLURRY PROCESSING Figure 5-28. Residual Oil-Based SGP Units (Source de Graaf andMagri2002 With permission Shell) The pellets could be burned directly or mixed in with fuel oil to make a liquid fuel known as carbon oil. The carbon oil could in part be used as feedstock for the gasifier, thus providing partial recycle of the carbon. This process had the advantage of being cheap and simple to operate. However, in the extraction process with fuel oil, the separation of soot from...

Gas Quench

The gas quench is used in the SCGP and the Prenflo processes. The raw synthesis gas, which has been cooled in the syngas cooler and freed of solids in a candle filter, is split into two approximately equal portions. One is recycled with a compressor and used to quench the gas leaving the gasifier from about 1500 to about 900 C, and the remaining net gas production is routed to further downstream processing. With gas cooling it is also possible to cool the gas further, to below 900 C, but in...

81 Oxygen Supply

The oxygen supply to a gasifier is one of the most expensive single parts of any gasification project. Cost estimates for various different IGCC projects put the ASU with its associated compressors at between 10 and 15 of the total plant cost. It also makes a significant contribution to overall operating costs, the power requirement for compression being of the order of magnitude of 5-7 of gross generator output. The arrangement for oxygen supply is one of the most important early decisions in...

Comparison Results

The results of various calculations are shown in Table 7-13, in which efficiencies are given for IGCC plants with fuel gas treating and with flue gas treating. In both cases efficiencies with and without CO2 removal are given. Some comparisons were already made in Section 5.3. The following additional conclusions can be drawn from these data The penalty in efficiency when including 90 CO2 removal as part of fuel gas treatment is 4-5 efficiency points. In all cases, flue gas treating could well...

23 Deductions From The Thermodynamic Model 231 Effect of Pressure

There is considerable advantage to gasifying under pressure, sufficiently so that practically all modern processes are operated at pressures of at least 10 bar and up to as high as 100 bar. The reasons for this are savings in compression energy and reduction of equipment size. To appreciate the realities of savings in compression energy, we can compare the energy required to provide 100,000 Nm3 h raw synthesis gas at 45 bar by either 1. gasifying at a relatively low pressure (5 bar) and...

662 Synthesis Gas Coolers

When the gas from a slagging gasifier is quenched to about 900 C, or where the gas is produced at temperatures in the 900 C to 1000 C range, it has to be cooled further before the gas can be treated for use. Two aspects of gas cleaning have to be considered carefully and intimately with the design of this section of the cooling system. These are particulate removal and condensation, whether it be condensation of tars from biomass gasification, for example, ammonium chloride from coal...

12 Gasification Today

The last ten years have seen the start of a renaissance of gasification technology, as can be seen from Figure 1-1. Electricity generation has emerged as a large new market for these developments, since gasification is seen as a means of enhancing the f) A A A S A o 1 o > A tP c ' c 1 c 1 Nq> v N > v N > v N > v N > v N< g> > f> > f> Nq > N< > N< > N< > N< > N< > Figure 1-1. Cumulative Worldwide Gasification Capacity (Source Simbeck and Johnson...

Supercritical Cycles

The biggest competition for gasification based power plants are advanced so-called supercritical steam cycles. These are called supercritical as both the maximum temperature and the maximum pressure of the steam are above the critical values of 374 C and 221 bar. By combining the benefits of the above features for improving the efficiency, the state-of-the-art steam cycles can now reach about 45 LHV basis for plants that are equipped with DeSOx and DeNOx facilities. The costs of these plants...

545 Process Safety Process Automation

Partial oxidation is a process that requires careful control and monitoring so as to ensure that accidental temperature runaways are avoided, especially during transient conditions such as start-up and shutdown. Process licensors have developed sophisticated control systems together with integrated automated start-up and shutdown procedures, which play an important role in safe operation. Butzert described the most important features of such systems in 1976. Each licensor includes details...

313 Char Gasification

The slowest reactions in gasification, and therefore those that govern the overall conversion rate, are the heterogeneous reactions with carbon, namely the water gas, Boudouard, and hydrogenation reactions already discussed in Chapter 2. The rates of reaction for the water gas and Boudouard reactions with char are comparable and are several orders of magnitude faster than for the hydrogenation reaction (Smoot and Smith 1985, p. 79). There are several different models describing the Boudouard...

841 The Claus Process

The basic Claus process for substoichiometric combustion of H2S to elemental sulfur was developed as a single-stage process on the basis of reaction 8-5 at the end of the nineteenth century. During the 1930s it was modified into a two-stage process in which initially one third of the H2S was combusted to SO2 and water, and in a second low-temperature catalytic stage, the SO2 was reacted with the remaining H2S to sulfur. Operating the second stage at a comparatively low temperature (200-300 C)...

823 Adsorption Systems

A second important group of gas treatment processes are based on the adsorption of impurities onto a solid carrier bed. Some of these processes, such as molecular sieve driers or pressure swing, allow in situ regeneration of the bed. Others, such as H2S chemisorption onto zinc oxide, cannot be regenerated economically in situ, and the beds require regular exchange. The quantity of a gaseous component, which can be carried by any particular adsorbent, depends not only on the characteristics of...

Names of Processes Plants and Companies

Over the course of time a number of technologies have changed owners or names, to the extent that this book could read like a Russian novel, where all the main characters go by at least three names. In order to simplify matters, we have used one name consistently throughout this book. In general, we have used the current names, but where this could cause confusion, we have used the name more generally associated with the particular technology. Name Used in Other Names or Owners Noell A...

417Petroleum Coke

Petroleum coke, more often named petcoke, is increasingly considered as an attractive feedstock for gasification, in particular as it becomes more and more difficult to fire this high-sulfur material as a supplemental fuel in coal-fired power stations. Apart from the feed systems that are similar to those for pulverized coal, the behavior of petcoke in gasifiers is very similar to that of heavy oil fractions. When gasified in certain entrained-flow slagging coal gasifiers, it is essential to...

622 Pumping Coal as a Coal Water Slurry

Pumping coal as a slurry is in principle and in practice a more elegant route to coal pressurization than lock hoppering. In water, coal concentrations of 60-70 wt can be used. A drawback is that only a small part of the water is required for the gasification, and the majority just constitutes a burden, as it has to be vaporized and heated to 1500 C. This in turn implies that the oxygen consumption is much higher than for dry-coal feed systems and that the CGE is substantially lower. For IGCC...

The Tophat Cycle Efficiency

The efficiency of the Tophat cycle is very dependent on the temperature difference between the hot turbine exhaust gases entering the recuperator and the humidified air leaving the recuperator. Typically for a 30 C decrease in the recuperator temperature difference there will be an increase of about one percentage point on the overall cycle efficiency. Also, in the Tophat cycle the turbine inlet temperature is a factor in relation to efficiency, although it should be realized that raising the...

412Coal Analysis

The methods generally used for specifying the analysis of coals has developed along pragmatic lines and are aimed at providing a useful guide to coal users rather than a purely chemical approach. The two types of analysis for any coal are the proximate analysis and the ultimate analysis. 1. Meta-anthracitie 2 Anthracite 3. Semianthracite 1. Low-volatile bituminous coal 2. Medium-volatile bituminous coal 3. High-volatile A bituminous coal 4. High-volatile B bituminous coal 5. High-volatile C...

415 Ash Properties

For all gasifiers the ash-softening and ash-melting or fusion temperatures are important variables. For fluid-bed gasifiers these properties govern the upper operating temperature at which agglomeration of the ash is initiated. For entrained-flow gasifiers it is essential to ensure that the ash flows continuously and that the slag tap does not freeze up. The method for determining these temperatures is specified in ASTM D1857, Fusibility of Coal and Coke Ash, or similar specifications, such as...

552 Twin Fluid Bed Steam Gasification The Silva Gas Process

This two-stage atmospheric biomass gasification process was developed by Battelle, and the first commercial demonstration unit with a feed capacity of 200 t d was built in Burlington, Vermont. Commercialization of the process has been taken over by Future Energy Resources (FERCO), who market it under the name of SilvaGas. The medium Btu gas at the demonstration unit is fired in an existing biomass fired boiler and is planned to be used later in a combustion turbine (Paisley, and Overend 2002)....

Molecular Sieves

The most common application of molecular sieves in connection with gasification plants is the removal of water and CO2 upstream of cryogenic units. Processes working at cryogenic temperatures, such as air separation or cryogenic gas separation, require a feed gas completely free of these components, which would otherwise freeze and deposit on the inlet heat exchangers and finally block them. The classic cycle described above is usually employed. In air separation duty, water and CO2 are not the...

71 Chemicals

The two chief components of synthesis gas, hydrogen and carbon monoxide, are the building blocks of what is often known as C1 chemistry. The range of products immediately obtainable from synthesis gas extends from bulk chemicals like ammonia and methanol, through industrial gases, to utilities such as clean fuel gas and electricity. Furthermore, there are a number of interesting by-products, such as CO2 and steam. As can be seen from Figure 7-1, many of these direct products are only...

Typical Concentrations

Typical concentrations of nitrogen compounds in various syngases are shown in Table 6-3. It is unclear whether the figure of 0.05ppmv NOx given by Rowles for oil gasification (Slack and James 1974) was really measured or just represents the limit of detect-ability. For raw gas from a Koppers-Totzek gasifier Partridge (1978) provides a figure of 70ppm NO. In the same source he gives a figure of 150ppm for the oxygen content. These are both much higher than figures quoted for other entrained-flow...

434 Development Potential Bio Oil

The major drawback of biomass is that the energy density is an order of magnitude lower than that of crude oil (Table 4-17). When it is further considered that biomass for fuel is a difficult to handle solid (grain is an exception in that it almost flows like water), this implies that fuel biomass can never be shipped economically over long intercontinental distances. Therefore, when contemplating really large biomass production, the first conversion that has to take place is to convert the...

572 MTCI Pulse Enhanced Steam Reformer

The MTCI process is based on steam gasification at about 600 C using indirect heat supply to the process via a heat exchanger built into the fluid-bed reactor. This has the advantage of operating at temperatures below the melting point of the smelt, but against this weighs the problem of tar production. The first 180 tDS d demonstration plant is being built at Big Island, Virginia and is due to start up in 2004. A number of conceptual issues such as sulfur removal still have to be resolved...

I

Multiple Hearth Furnace Equipment Performance SGP is a reliable process that has been proved in many applications worldwide. This reliability is based on the use of proven equipment in critical duties. Typical lifetimes are listed in Table 5-12 (Higman 1994). Table 5-12 Typical SGP Equipment Lifetimes SGP employs a sophisticated automatic start-up and shutdown system. Since But-zert's description of the main characteristics (Butzert 1976), further developments include, for example,...

Membrane Walls

The alternative to refractory linings is a water-cooled membrane wall construction such as that shown in Figure 6-6. The design shown is that of the Noell reactor, but it is typical also of other entrained-flow slagging gasifiers such as SCGP and Prenflo. The membrane wall consists essentially of high-pressure tubes, in which steam is generated, connected by flat steel bridges of which the width is about equal to the outer diameter of the tubes. Tubes and bridges are welded together into a...

524 Circulating Fluid Bed CFB Processes

The characteristics of a circulating fluid bed combine many advantages of the stationary fluid bed and the transport reactor. The high-slip velocities ensure good mixing of gas and solids, and thus promote excellent heat and mass transfer. Small particles are converted in one pass, or are entrained, separated from the gas, and returned via an external recycle. Larger particles are consumed more slowly and are recycled internally inside the bed until they are small enough for external recycling....

522 The Winkler Process

The Winkler atmospheric fluid-bed process was the first modern continuous gasification process using oxygen rather than air as blast. The process was patented in 1922 and the first plant built in 1925. Since then some 70 reactors have been built and brought into commercial service with a total capacity of about 20 million Nm3 d (Bogner and Wintrup 1984). This process is now, however, only of historic interest, since all but one of these plants has been shut down almost entirely for economic...

Over the Fence

Even in locations where no pipelines are available, it is possible to buy oxygen over the fence. In this business model, which has a long tradition in oxygen supply to the steel industry, a gas supply company will own and operate a dedicated air separation unit within the gasification complex. By-products such as argon, which may be of little interest to the gasifier operator, can make such an arrangement very attractive. The specialist, operating know-how of the gas companies enable them to...

699 Mercury

Mercury can be present in both coal and natural gas, although the quantities vary widely from source to source. Mercury presents a potential hazard both for the integrity of the plant and as a toxic emission for the environment. Whether gasifying coal or partially oxidizing natural gas, mercury from the feed will appear at least in part in the synthesis gas, and so for these feeds it is necessary to address this feed contaminant. Wilhelm describes a number of different mechanisms by which...

Flue Gas Recycle

The potential of flue gas recycle is a neglected area of cycle design. It has significant advantages for natural gas-fired gas-turbine-based power generation (including IGCC) where gaseous components, for example, CO2, have to be removed from the flue gas as well as in terms of extremely low thermal NOx emissions. Before discussing its use in syngas applications we will review its effect on a natural gas-fired combined-cycle plant. The basic concept is to replace most of the excess air to the...

43 Biomass

The term biomass covers a broad range of materials that offer themselves as fuels or raw materials and that have in common that they are all derived from recently living organisms. This definition clearly excludes traditional fossil fuels, since although they also derive from plant (coal) or animal (oil and gas) life, it has taken millions of years to convert them to their current form. For the purpose of this book, we have chosen to include all agricultural and forestry wastes as well as...

242 Optimum Operating Point Efficiencies

There are a number of different criteria that are frequently quoted for gasification processes (Reimert 1989). The two most commonly encountered are cold gas efficiency (CGE) and carbon conversion. The definitions are ., _ . Heating value in product gas MW . __ Cold gas efficiency -- . . , , x 100 whereby it is important always to clarify whether the heating values are on a higher heating value (HHV) or lower heating value (LHV) basis. Carbon conversion is defined as , i. Carbon in gasification...

693Chlorine Compounds

Chlorine compounds are present in most coals. They will react with ammonia in the raw gas to form ammonium chloride (NH4Cl). At high temperature this is (dissociated) in the vapor phase, but below 250-280 C it becomes solid and presents a fouling risk to the gas cooling train. At lower temperatures still, below the water dewpoint of the gas, it goes into solution and is highly corrosive. These aspects have to be considered in the design of the cooling train. Metals in the feedstock will also...

Nnnnnnnnnn itf

O A it A A oP o 1 of1 o > dP oil' oi' of1 o 1 > v kQ> v x< r x< r x< r x< r > > > > Figure 4-2. Growth of Hydrogen and Power Applications for Gasification of Liquid and Gaseous Feedstocks (Source SFA Pacific 2001) stocks, but must be considered in the design of the preheat train. It is important in this connection, however, to ensure that abrasive solids are kept to a minimum. The feedstock must be maintained within certain viscosity limits at critical points in the...

535 The Texaco Process

The Texaco gasification process was developed in the late 1940s. Although the main focus at that time was on utilization of natural gas reserves, some work on coal gasification was also performed (Schlinger 1984). The process achieved commercialization initially with gas feed (1950) and later with liquids (1956). This technology is discussed in more detail in Section 5.4. Against the background of a perceived medium-term oil shortage at the beginning of the 1970s, the previous work on coal...

Process Description

The heart of the Lurgi process is in the reactor, in which the blast and syngas flow upwards in counter-current to the coal feedstock (Figure 5-1). Coal is loaded from an overhead bunker into a lock hopper that is isolated from the reactor during loading, then closed, pressurized with syngas, and opened to the reactor. The reactor is thus fed on a cyclic basis. The reactor vessel itself is a double-walled pressure vessel in which the annular space between the two walls is filled with boiling...

531 General Considerations Dry Coal Feed Gasifiers

As discussed in Chapter 2, dry-coal feed gasifiers have the advantage over coal-water slurry feed gasifiers in that they can operate with almost the minimum amount of blast. This implies in practice that they have a 20-25 lower oxygen consumption than coal-water feed gasifiers. Also, as shown in Section 2.4, dry-coal feed entrained-flow gasifiers have in principal an additional degree of freedom that makes it possible to better optimize the synthesis gas production. Moreover, it is possible to...

544 New Developments

Despite various improvements over the years, it is generally recognized that handling of the soot produced by partial oxidation of heavy residues places a considerable financial burden on the overall process. This has caused operating companies and others to investigate alternatives. In the 1970s one operating company was already using a toluene extraction process to recover the soot as saleable carbon black. A number of other companies made similar attempts, but the economics of these...

Basis for Calculations

All calculations were based on a typical internationally traded coal of which the properties are given in Table E-1. All flow schemes are based on 100 kg maf coal, and the relevant mass and energy values are all based on this quantity. Taking the mass values per second we get the energy flows in MW. For drying the coal from 12.5 to 2 moisture 31 MJth are required. As this heat is supposed to be supplied by burning part of the clean fuel gas, this corresponds to an energy penalty of about 19MJe....

Gasifier Outlet Temperature as a Function of the Gas Analysis

Calculating the gasifier outlet temperature from the gas analysis is not so simple. The reason is that it is not possible to measure the composition of the gas when it leaves the reactor. The best one can do is a postmortem when the gas has been cooled down. There have been attempts to devise a means to draw a gas sample directly after the gas has left the reactor through a cooled, high-alloy, thin tube and then perform the analysis. The idea is that by freezing-in the equilibria between the...

921 Gaseous Effluents

The principal gaseous effluents arising from the use of fossil fuels are oxides of sulfur and nitrogen and particulate matter. Others that require attention are not fully combusted components, such as carbon monoxide. Currently in gasification systems the first three components are all removed in the intermediate fuel gas, where sulfur and nitrogen are present as reduced species and in higher concentrations than would be the case in flue gas. Both features make removal of these species to low...

442 Liquid Wastes

Organic wastes from chemical production vary as widely as the processes from which they originate. One published example is the feedstock to a waste gasification plant at Seal Sands (United Kingdom), which processes streams from caprolactam and acrylonitrile production. These waste streams include mixtures of nitriles and amines as well as cyanide and ammonia compounds. The differences in the characteristics of these streams, the flow rates of which can vary...

Liquid Oxygen Storage

Some storage of liquid oxygen is always required in IGCC power stations in order to cope with sudden changes in demand. In order to use the oxygen for peak shaving, generally a much larger storage capacity is needed. This does increase the capital cost of the plant, but it has the advantage that the ASU does not have to be designed for the peak demand but for the average daily demand. So it is a matter of balancing these two cost items against each other. It should be mentioned that apart from...

532 The Koppers Totzek Atmospheric Process

Just as with moving-bed and fluid-bed processes, the first entrained-flow slagging gasification process operated at atmospheric pressure. The atmospheric pressure Koppers-Totzek (KT) process was developed in the 1950s, and commercial units were built in Finland, Greece, Turkey, India, South Africa, Zambia, and elsewhere, mostly for ammonia manufacture. The South African unit has been reported as achieving a 95 availability (Krupp-Koppers 1996). In recent years no new units of this type have...

543 Lurgis Multipurpose Gasification Process MPG

Lurgi has maintained a leading position in coal gasification since the 1930s, but for many years worked as contractor and licensing agent for the Shell SGP process for partial oxidation of liquids and gases. In 1998 Lurgi announced that it would now be marketing its own technology under the name of LurgiSVZ multipurpose gasification MPG Figures 5-31 and 5-32 . This technology had been in existence since 1969 at what is today SVZ Schwarze Pumpe Hirschfelder, Buttker, and Steiner 1997 . It was...

584Hydrogasification

During the 1970s and 1980s there was considerable interest in developing a process to produce synthetic natural gas by direct hydrogenation of coal to methane. The principle reaction involved is that of methanation. C 2H2 S CH4 -75 MJ kmol 2-6 The thermodynamics of this reaction demand that it be operated at high pressure. Although the reaction is exothermic, the reactants must first be brought to a high temperature for the reaction to proceed at an economically acceptable rate. Furthermore,...

Wet Cataiysis

Processing H2S to sulfuric acid differs from conventional acid plants whether using sulfur or metallurgical off gases as feed in that water is already present in the converter. This water reacts immediately with the SO3 formed there and therefore demands a totally different approach to the recovery of liquid acid compared with a standard double absorption unit. The H2S component of the acid gas is first combusted with excess oxygen to form SO2 and water see Figure 8-18 . The excess is selected...

523 The High Temperature Winkler HTW Process

The name high-temperature Winkler for the process developed by Rheinbraun primarily for lignite gasification is to some extent a misnomer. The most important development vis- -vis the original Winkler process is the increase of pressure, which has now been demonstrated at 30 bar. Rheinbraun, an important lignite producer in Germany, began work on the process in the 1970s. A Rheinbraun subsidiary, Union Kraftstoff, Wesseling, had operated atmospheric Winkler generators between 1956 and 1964, and...

541 The Texaco Gasification Process

The Texaco Gasification Process was developed in the late 1940s. Early research efforts focused on producing syngas from natural gas to produce liquid hydrocarbons via Fischer-Tropsch technology. The first commercial-scale plant based on natural gas as a feedstock was commissioned in 1950 for the production of ammonia. The first commercial-scale use of oil feedstocks occurred in 1956, and early coal work began at about the same time. In the 1970s research efforts were then focused on coal...

6114 Metal Dusting

Metal dusting is a particularly aggressive form of high-temperature mostly CO corrosion, which has received particular attention in connection with the manufacture of CO-rich synthesis gases using steam reforming or catalytic partial oxidation. Although certain details of the mechanism of metal dusting, and particularly the potential for countermeasures, remain the subject of some debate, the essentials have been understood for many years Hochmann 1972 Grabke, Brach-Troconis, and M ller-Lorenz...

Literature Data Bank

The literature databank gaslit.mdb contains over 500 entries on the topic of gasification, including all the literature cited in this book. It includes titles, authors, and keywords for all papers presented at the Gasification Technologies Council Conferences since 1998, all the IChemE Gasification Conferences, and a number of other important sources not normally accessible to nonparticipants. The database includes a keyword-based search facility, with up to six specified keywords per article....

Flow Scheme

The flow scheme of the Tophat cycle is shown in Figure 7-20 van der Burgt and van Liere 1996 . The water is injected in the air A entering the compressor in such a way that the compressor does not suffer from a parasitic pressure drop. It is injected in the form of very fine droplets of a mean diameter of about 1-3 These droplets, that can be made by combining flash evaporation with efficient atomizers as in the swirl flash technology van Paassen and van Liere 1980 , are so small that the...

High Temperature HT Shift

Conventional high temperature shift uses an iron oxide-based catalyst promoted typically with chromium and more recently with copper. The operating range of these catalysts is between 300 and 500 C. Much above 500 C sintering of the catalyst sets in and it is deactivated. HT shift catalyst is tolerant of sulfur up to a practical limit of about 100ppmv, but it is likely to loose mechanical strength, particularly if subjected to changing amounts of sulfur. An important aspect in the design of CO...

331 Modeling

The systems described in this chapter are extremely complex, which has to date placed limitations on the application of kinetic models to commercial gasification reactor design. Nonetheless the availability of increasingly powerful computers with a deeper understanding of the physical and chemical processes of coal combustion Figure 3-8. CFD Model of a Gasification Burner Outlet Zone Source Hofmockel, Liebner, and Ulber 2000 Figure 3-8. CFD Model of a Gasification Burner Outlet Zone Source...

233 Fuel Footprint

For a good understanding of the gasification of any particular feedstock, whether coal, heavy oil, waste biomass, or gas, it is important to calculate the gasification characteristics of the fuel in order to be able to understand what is going on in the reactor and to optimize the reaction conditions. Figure 2-3. Variation of Syngas Compositions with Pressure at 30 bar Figure 2-3. Variation of Syngas Compositions with Pressure at 30 bar Figure 2-4. Variation of Yields with Pressure at 30 bar...

221 Basic Data

A model for gasification is only as good as the basic thermodynamic data used. To ensure consistency of mass and heat balances it is of fundamental importance to limit the data set to a minimum and generate all other data from this. In the calculations used in this book and in the website programs, use has been made of various sources, the most important being Barin 1989 . For the thermodynamic calculations standard enthalpy and entropy data have been used in combination with a curve-fit for...