Patent Application
20070275278
A new and novel integrated generator for generating electricity is provided. The new process comprises introducing a fuel mixture into a reaction zone, reacting the fuel mixture to produce a first stream comprising steam, feeding said first stream from said reaction zone to a turbine or a turbo charger, and generating electricity with said turbine.
A new and novel integrated system for generating electricity is also provided. The system combines several integrated generators in series and each generator comprises a reaction zone for introducing and reacting a fuel mixture to produce a reformate stream and a turbine in communication with said reaction zone for the generation of electricity from said reformate stream. To improve thermal efficiency and eliminate pollution, additional controlled amount of air and/or fuel can be injected into the feed mixture of the next reformer (i.e. reaction zone).
In the first step of the process of the present invention, a fuel mixture is introduced into a reaction zone. The fuel mixture may comprise fuels, steam and an oxygen containing gas. The fuels may be any C1-C16 hydrocarbons, C1-C8 alcohols, vegetable oils, bio-ethanol, bio-diesel; any fuels derived from biomass or from agriculture/industrial/animal wastes etc. Typical useful fuels which can be oxidized by a catalytic reactor into reformate include but are not limited to natural gas, biomass waste gas, LPG, gasoline, diesel, bio-ethanol, bio-diesel, corn oil, olive oil, soybean oil, methanol, ethanol, propanol, butanol, biobutanol etc.
The oxygen containing gas may be air, oxygen or any other gaseous mixture, which contains oxygen.
The fuel, steam and oxygen containing gas may be mixed prior to feeding into the reaction zone, or may be fed separately into the reaction zone. Even if the reactants are introduced into the reaction zone separately, they become mixed in the reaction zone, and thus, this embodiment is still encompassed by the language used herein that the fuel mixture is introduced into the reaction zone.
Any conventional reactors may be used as the reaction zone. The reactor may take the form of a reformate generator or a reformer.
The reaction zone includes a catalyst composition, which can be a catalyst unsupported or supported with any known supports. If supported, the support material is preferably a substantially inert rigid material, which is capable of maintaining its shape, surface area and a sufficient degree of mechanical strength at high temperatures. Examples of viable catalyst support materials include but are not limited to alumina, alumina-silica, alumina-silica-titania, mullite, cordierite, cerium oxides, zirconium oxide, cerium-zirconium-rare earth oxide composite, zirconia-spinel, zirconia-mullite, silicon carbide and other oxide composite thereof.
The catalyst composition includes at least one metal catalyst component such as platinum, palladium, rhodium, iridium, osmium and ruthenium or mixtures thereof. Other metals may also be present, including the base metals of Group VII and metals of Groups VB, VIB and VIB of the Periodic Table of Elements (e.g., chromium, copper, vanadium, cobalt, nickel, iron, etc).
The catalyst composition in the reaction zone serves to facilitate or promote reactions between the fuel, steam and oxygen containing gas mixture. More description on the reforming of diesel oil into hydrogen by an autothermal reformer is provided in U.S. Pat. No. 4,522,894, which is hereby incorporated by reference. Multiple reactions, including steam reforming, partial oxidation, combustion, water gas shift etc. may occur simultaneously in the same reaction zone (i.e. reformer).
Because the catalysts are prone to deactivation and breakdown at high temperatures (e.g., exceeding 1200° C.), it is preferred that the reaction zone be kept at temperatures between 150-1200° C., preferably between 150-1000° C. To initiate the reaction, the fuel mixture or the reaction zone may be preheated using any known conventional means to a temperature between 150-600° C.
In the present invention, the fuel mixture is reacted over catalyst to form a first stream comprising steam (preferably >20%), one or more of H2, CO, CO2, N2, CH4, O2 and unconverted hydrocarbons. To produce high temperature and pressure reformate stream in the first stream, two key ratios must be monitored in the fuel mixture: a) H2O to C ratio and b) O2 to C ratio. More specifically, it is preferred that the H2O to C ratio be greater than 1 (preferably between 2 and 50) and the O2 to C ratio be over 0.15 (preferably between 0.2 and 20). Since the latent heats of all useful fuels vary in a wide range and the oxidation reactions over Pt group catalysts of every fuel mentioned in this invention are very fast, these ratios should be adjusted individually and/or simultaneously depending on the specific fuel mixture composition to keep the reactions above a minimum operating temperature, and also to limit the reformer's maximum operating temperature below 1200° C. (preferably below 1000° C.). The adjustments of these two ratios to control the reaction zone temperature can be within and/or outside the operating ranges mentioned previously and are within the skills of one skilled in the art.
For example, when methane is used as the hydrocarbon fuel, the following reactions are known to occur:
Catalytic Combustion: CH4+2O2→CO2+2H2O
Catalytic Partial Oxidation Reaction: CH4+½O2→CO+2H2
Steam Reforming Reaction: CH4+H2O→CO+3H2
Water Gas Shift Reaction: CO+H2O→CO2+H2
On the other hand, when ethanol is the fuel, the following reactions occur:
Complete Combustion: C2H5OH+3O2→2CO2+3H2O
Catalytic Partial Oxidation: C2H5OH+½O2→2CO+3H2
Thus, different fuels result in different amounts of CO2 and water (e.g. steam).
Different fuels also result in different amount of heat being produced. For example, while the catalytic partial oxidation reaction for methane is an exothermic reaction, the catalytic partial oxidation reaction for ethanol is an endothermic reaction.
One skilled in the art would thus appreciate that different O2/C and H2O/C ratios are needed for optimal operating conditions in the reaction zone (i.e. 150-1200° C.) due to the difference in oxidation reaction heats and product quantity.
Once the fuel mixture is reacted to produce a first stream reformate comprising steam, and one or more of H2, CO, CO2, N2, O2 and unconverted HC, the first stream is fed into a turbine or a turbo charger to generate electricity. The turbine or turbo charger is thus said to be in communication with the reaction zone.
Turbine refers to any conventional electrical generator for which a gaseous feed (preferably high pressure gas) is used to drive the turbine to produce electricity. Turbine includes any electric generator components in communication with the actual turbine draft shaft. The most common form is a steam turbine, in which steam is used to drive the steam turbine to generate electricity.
Thus, in the exemplary embodiment of the present invention, the first stream comprising steam is fed into the turbine to generate electricity. A first stream comprising a higher percentage of steam (e.g., at least 30%, 50%, 75%) may also be used.
The first stream may be fed into the turbine via injection or any other conventional means.
Using the teachings of the present invention, a number of different generator and system configurations are available to one skilled in the art.
For example, as shown in an exemplary embodiment in
Since there may be H2, CO and unreacted fuels (i.e. hydrocarbons or alcohols) present in the first stream due to insufficient oxygen in the first feed mixture, there is further shown a second reaction zone 15 in
In
The following examples are based on thermodynamic calculations using the HSC Chemistry Version 4.1 software (Outokumpu Research Oy, Pori, Finland). For example, the equilibrium gas composition for a given fuel feed mixture is first calculated at temperatures between 100 and 2500° C. The calculated equilibrium composition at a given temperature is then used to calculate the adiabatic temperature raise from the initial gas temperature at 100° C. However, it is found that, over a certain temperature range, the equilibrium composition is a strong function of temperature, i.e. a small change in temperature will cause a large change in equilibrium composition and thus affect the calculated adiabatic temperature (Tad). Therefore, the equilibrium composition at a given temperature and the calculated adiabatic temperature (Tad) for this composition should be iterated continuously until these two temperatures are finally matched. However, to demonstrate the effects of H2O/C and O2/C ratios on the reactor's operating temperature, and the importance of controlling these two ratios, satisfactory conclusions can be reached by using the approximate calculated values (+/−50° C.) as shown in the following tables.
100 moles of various hydrocarbon mixtures comprising various amounts of methane and air are fed and reacted in the reaction zone. No water is used in this example. The calculated results from the Chemistry Version 4.1 software are summarized in Table 1.
This table lists the adiabatic temperature (Tad) as a function of % CH4 (dry), and the product gas composition as a function of O2/C ratio. For O2/C ratios of 4.20 and 2.10, complete combustion reactions can be expected thermodynamically since all CH4 are converted to CO2, and the adiabatic temperatures after combustion are 12000 and 1980° C. respectively. As the O2/C ratios is shifted toward the lower values, more H2 and CO and less amount of CO2 are produced, indicating that the reaction mechanism is gradually shifting from the complete combustion reactions toward the partial oxidation reactions, and the calculated adiabatic temperatures are also gradually reduced to <1000° C. Therefore, it would have been preferred to keep the O2/C ratio below 0.84 for this methane/air system to avoid catalysts being thermally deactivated and/or melted.
As shown in Example 1, a sudden momentary increase in O2/C ratio to a value over 1.05 can cause the catalyst's temperature over 14000° C., this will cause permanent damage and/or even melt the catalyst. Furthermore, low O2/C ratios will produce coke (i.e. C). Thus, Example 1 confirms that U.S. Pat. No. 6,960,840, which utilized methane combustion without water in the feed gas, is susceptible to thermal deactivation, coking and/or melting of its catalysts if the O2/C ratio is not controlled properly.
Example 1 is repeated, except 100 moles of water are added to the same 100 moles of CH4 and air mixture. The calculated adiabatic temperature raise (Tad, degree C.) and the gas composition are summarized in Table 2.
By comparing Tables 1 and 2, under the exact CH4/air mixture, the addition of water will reduce the adiabatic temperature and avoid coke formation. Thus, Table 2 confirms that
the use of steam in the feed gas is a useful improvement over Example 1. It is believed that steam, which has a higher heat capacity compared to other gases, absorbs reaction heats more efficiently to keep all adiabatic temperature below 1200° C. Furthermore, the addition of water to the feed mixture will shift the equilibrium composition, avoid coke formation and will favor easier and more flexible reformer operations. Thus, the catalyst life can be extended with the use of steam in the feed.
Example 1 is repeated except that 200 moles of water are added to the same 100 moles of CH4 and air mixture. The calculated adiabatic temperature (Tad, degree C.) and the gas composition are summarized in Table 3.
Compared to Example 2, Table 3 shows that an additional 100 moles of water further reduces the adiabatic temperature in the reaction zone. Table 3 illustrate that in some cases (i.e. low O2/C ratios), the reactor temperatures are too low, indicating that catalysts may lost their activities due to low operating temperatures and may have problems of producing high-pressure reformate. Thus, Table 3 confirms the importance of maintaining control and optimizing the O2/C and H2O/C ratios of the feed gas.
Example 1 is repeated except that ethanol was used as the fuel source instead of methane. The results of these thermodynamic calculations are shown in Table 4.
As shown in Table 4, the adiabatic temperatures for the O2/C ratios between 2.10 and 0.70 rose over 1400° C. and, thus, the catalysts will melt and/or become thermally deactivated. Even for the O2/C ratio of 0.26, there is a risk of catalyst deactivation as a result of carbon formation, which will block the catalyst bed and cause flow disturbance. Therefore, like Example 1 with methane, Table 4 confirms that the use of ethanol and air without water/steam in the feed mixture does not lead to a thermally efficient or successful long operation for a catalytic reformer.
Example 4 is repeated, except 100 moles of water are added to 100 moles of ethanol and air mixture. The results of the thermodynamic calculations are shown in Table 5.
Table 5 shows that, with the addition of steam, the adiabatic temperatures under various O2/C ratios remain below 1150° C. and there is no carbon formation, thereby indicating more favorable operating conditions for the catalysts in the reaction zone. Furthermore, because of the difference in latent heat, the results of Tables 2 and 5 indicate that the optima O2/C ratio to limit the reactor's temperature <1000° C. varies with the fuels used.
For example, Table 5 shows that for a feed mixture containing 13.04 moles of ethanol, 18.26 moles of O2, 68.70 moles of N2 and 100 moles of water (H2O/C=3.83, O2/C=0.70), the feed ethanol over the Pt group catalysts is converted completely, and the first stream will contain 68.7 moles of N2, 104.0 moles of steam, 35.40 moles of H2, 6.34 moles of CO and 19.7 moles of CO2.
Example 4 is repeated, except 200 moles of water are added to 100 moles of ethanol and air mixture. The results of the thermodynamic calculations are shown in Table 6.
Like Example 3, Table 6 again confirms the reduction of operating temperatures and catalytic activities when excess H2O is added. Again, the optima operating H2O/C and O2/C ratios to limit the reactor's temperature <1000° C. vary with the type of fuels used.
Example 7 illustrates the use of a new integrated two-generator system as shown in
As shown in Table 2, a gas mixture containing 16.67 moles CH4, 17.5 moles O2, 65.83 moles of N2 and 100 moles of water (H2O/C=6.0 and O2/C=1.05) are injected into the first new integrated generator 19 as shown in
After driving the Turbine 20, the reformate gas will lose its pressure and temperature. Since the vent reformate gas from Turbine 20 still contains H2 and CO, additional make-up air in the amount of 15.83 moles is added into this gas stream and the mixture is injected into the Second integrated generator 19a to recover the latent heats as shown in
If the second integrated generator 19a cannot completely combust the intermediate products such as H2 and CO and unconverted fuels or HC, a third integrated generator (not shown) can be added in series. In this case, additional controlled amount of air can be injected into the inlet feed mixture of this third integrated Generator. Again, the oxidation reactions can recover all latent heats to improve the system's overall thermal efficiency. Furthermore, to make sure that the final vent gas is pollution free, excess amount of air can be added into the feed stream of the last generator of the integrated system to combust all H2, CO and HC. If necessary, a controlled amount of fuel can also be injected into the feed stream to keep the reaction zone's temperature above its minimum operating temperature and, thus, maintain the catalyst's activity and the oxidation reaction rates.
This application claims benefit to and priority of U.S. Provisional Application No. 60/808,986 filed May 27, 2006, herein incorporated by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 60808986 | May 2006 | US |
