Patent Application
20100242478
The present disclosure relates, in general, to methods and systems for generating heat by combusting sulphur and, in particular, to methods and systems for combusting sulphur with no, or very minimal, harmful emissions to the environment.
The production of electric power from fuel is based on the conversion of the latent chemical combustion energy of fuel into heat, with subsequent conversion of heat into mechanical energy and to electric energy. Hydrocarbons such as coal, natural gas, and petroleum products are the most commonly used fuels however its combustion is accompanied by the emission of carbon dioxide (CO2) which, until recently, was thought to be harmless but has subsequently been found to have a major deleterious effect on global warming. Most fossil fuels also contain sulfur compounds in various forms. Combustion of fuels containing sulphur produces, in addition to CO2, sulphur dioxide (SO2). SO2 dissolves in water vapor to form acid, and interacts with other gases and particles in the air to form sulfates and other products that can be harmful to people and the environment.
On the other hand, aside from hydrocarbons, sulphur is the only other naturally occurring material from which energy can be harnessed by combustion. Despite this fact, the use of sulphur compounds as a source of energy has been largely ignored.
Burning sulfur in pure oxygen in stoichiometric quantities produces extremely high temperatures of more than 5,000° C. The calculated flame temperature when the reactants (SO2, SO, S2, S and O2) are in equilibrium, taking into account dissociation processes, is about 3000-3500° C.
An innovative method and system for combusting sulphur with no harmful emission of carbon dioxide to the environment can be used for a variety of applications, including power generation, the production of elemental sulphur, and the production of carbon monoxide. In general, sulphur is evaporated by reaction of oxygen with liquid sulphur that is maintained in the region of its auto-ignition temperature which is about 260° C. Oxygen and liquid sulphur immediately react to form sulphur dioxide but, because the liquid sulphur is heated continuously by the combustion reaction, substantial amounts of sulphur are vaporized into the sulphur dioxide containing gas leaving the liquid sulphur:
S8 liquid(260° C.)+O2 gas→SO2 gas+heat+3S2 vapor (1)
Subsequently, the thermodynamic energy contained in the sulphur vapor (S2) is converted into heat energy through stoichiometric (or near-stoichiometric) interaction with oxygen:
S2+2O2→2SO2+heat (2)
Because of the chain character of the burning process, the sulphur vapor (S2) burns in oxygen in tenths of a second attaining a temperature level close to the theoretical adiabatic temperature of about 3000-3500° C. This high temperature is a key element of the process as it provides a major pathway for complete reduction of sulphur dioxide by carbonyl sulphide (COS) to carbon dioxide and sulphur vapor according to overall equation (3):
SO2+2COS→2CO2+3/2S2 (3)
The carbonyl sulphide (COS) can be generated by chemical reaction between a supply of hydrogen sulphide (H2S) flowing into the system and a supply of recycled carbon dioxide in which the H2S is converted to COS and water (H2O):
H2S+CO2→COS+H2O (4)
In terms of material balance, the mass equivalent of sulphur, oxygen and hydrogen sulphide that enter the system are removed from the system in the form of recovered elemental sulphur and water. Not only is the elemental sulphur a useful product, but the water in the form of steam can be used to do useful work or generate power.
This sulphur combustion method and system produces with minimal if any harmful emission of sulphur dioxide to the environment due to reduction of sulphur dioxide to sulphur vapor and carbon dioxide (either at high temperature or catalytically at low temperature). In one main implementation of this technology, the entire amount of carbon dioxide that is generated from the reduction of sulphur dioxide is recycled to regenerate carbonyl sulphide, thus providing a “zero-carbon emission” combustion method and system. This “zero-emission” system can be configured to leak no carbon to the environment or, in other embodiments, it may be configured to allow only a very small amount of carbon to the atmosphere.
In other words, a method and system for combusting sulphur combustion is unimpeded by sulphur oxides. This method of harnessing energy from sulphur combustion is due to the reduction of sulphur dioxide by carbonyl sulphide. In one main implementation of this technology, the entire carbon dioxide generated through this reduction reaction of sulphur dioxide is recycled to regenerate carbonyl sulphide, thus providing a so-called “zero-carbon emission” combustion method and system. In terms of material balance, the mass equivalent of sulphur, oxygen and hydrogen sulphide that enter the system are removed from the system in the form of recovered elemental sulphur and water.
In accordance with one aspect of the present invention, a method for the conversion of the latent chemical combustion energy of sulphur into heat with minimal, if any, harmful emissions to the environment comprises combusting sulphur vapor (S2) in oxygen (O2) in a combustor/reactor and subsequently reacting sulphur dioxide (SO2) with carbonyl sulphide (COS) to yield combustion gases comprising carbon dioxide (CO2) and sulphur vapor (S2). The method may further comprise providing one or more heat recovery and sulphur condensation units for recovering heat from the combustion gases and for condensing the sulphur vapor to yield recyclable carbon dioxide (CO2), elemental sulphur (S), liquid S8, and steam for any number of industrial applications or for power generation. The heat recovery and sulphur condensation units can be separate units or combined as a single unit that performs both heat recovery and condensation functions.
In accordance with another aspect of the present invention, a method for generating thermodynamic energy from sulphur combustion comprises catalytically reducing sulphur dioxide (SO2) in the presence of carbonyl sulphide (COS) to generate carbon dioxide and sulphur vapor (S2), condensing the sulphur vapor to yield liquid sulphur, evaporating the liquid sulphur to generate sulphur dioxide gas and sulphur vapor, combusting the sulphur vapor with oxygen gas (O2) to generate hot sulphur dioxide gas, mixing in an ejector the hot sulphur dioxide gas with cooler, lower-pressure sulphur dioxide gas that is recycled from downstream of at least one turbine, and harnessing energy in the sulphur dioxide gas that emerges from the ejector.
In accordance with yet another aspect of the present invention, a method for hydrogen sulfide (H2S) conversion to elemental sulphur and water comprises steps of evaporating liquid sulphur to generate sulphur dioxide (SO2) gas and sulphur vapor (S2) and combusting the sulphur vapor (S2) with oxygen gas (O2) to generate heat. The method further comprises a step of reducing at high temperature the sulphur dioxide (SO2) to carbon dioxide (CO2) and sulphur vapor (S2) by reacting the sulphur dioxide (SO2) with carbonyl sulfide (COS). The COS may be generated by reacting hydrogen sulfide (H2S) with recycled carbon dioxide (CO2) that is recycled by condensing sulphur vapor and carbon dioxide to yield liquid S8, elemental sulphur (S), and CO2. The method may further comprise a step of heat recovery to produce steam. The steam can be used, for example, to drive a turbine to generate electricity.
In accordance with yet another aspect of the present invention, a method for transporting sulphur in form of COS gas by pipeline comprises steps of receiving hydrogen sulphide (H2S) and carbon dioxide (CO2) into a carbonyl sulphide (COS) generator and generating COS and H2O. The COS can then be transported, for example by pipeline, to a sulphur-recovery plant at a remote location for subsequent recuperation of elemental sulphur and energy generation according to one or more of the methods described herein.
In accordance with yet a further aspect of the present invention, a method for generating carbon monoxide comprises a step of interacting at high temperature carbonyl sulphide (COS) with sulphur dioxide (SO2) in the presence of carbon dioxide (CO2) to yield S2, and carbon monoxide (CO) as a predominate gas. The sulphur dioxide (SO2) and heat are results of sulphur vapor (S2) combustion in oxygen (O2). The method then entails rapidly cooling the S2, and CO while condensing the S2 in order to transform the S2 into liquid sulphur (S8) and elemental sulphur (S), and to prevent CO and S2 re-associating to form COS. Optionally, a further step involves separating the CO from the remaining CO2. This is a useful emission-free method for producing CO for any number of industrial applications.
In accordance with yet another aspect of the present invention, a system for burning sulphur has a combustor/reactor for combusting/reacting sulphur dioxide (SO2), sulphur vapor (S2), carbonyl sulphide (COS) and oxygen (O2) to yield hot combustion gases comprising carbon dioxide (CO2) and sulphur vapor (S2). The system also has an ejector disposed downstream of the combustor/reactor for reducing a temperature and pressure of the hot combustion gases by exchanging heat and pressure with a supply of carbonyl sulphide. The system also has a carbonyl sulphide generator for generating the carbonyl sulphide supplied to the ejector.
In accordance with yet another aspect of the present invention, a method for the conversion of the latent chemical combustion energy of sulphur into heat without causing harmful emissions to the environment comprises steps of evaporating liquid sulphur to generate sulphur dioxide (SO2) gas and sulphur vapor (S2) and combusting the sulphur vapor (S2) with oxygen gas (O2) to generate heat. The sulphur can be evaporated and the sulphur vapor oxidized under a pressure, for example, of 1 to 35 atmospheres. The system may also have an ejector disposed downstream of the combustor for heat and pressure exchange between the hot and pressurized sulphur dioxide (SO2) and the low-temperature, unpressurized carbonyl sulphide which results in generation of a high-energy working medium comprising sulphur vapor and carbon dioxide. The method further comprises a step of harnessing the energy of this working medium through gas and steam turbines, for example to generate electricity.
In accordance with yet another aspect of the present invention, a system for burning sulphur comprises a combustor for combusting sulphur vapor (S2) and oxygen (O2) to yield hot combustion gases comprising sulphur dioxide (SO2). The system also comprises an ejector disposed downstream of the combustor for reducing a temperature and pressure of the hot combustion gases by exchanging heat and pressure with a supply of recycled sulphur dioxide gas to generate a stream of sulphur dioxide gas at a reduced temperature and pressure, wherein the recycled sulphur dioxide gas is recycled from downstream of at least one turbine that harnesses energy from the stream of sulphur dioxide emerging from the ejector.
Traditionally, the production of electric power from fuel is based on the conversion of the latent chemical combustion energy of fuel into heat, with the subsequent conversion of heat into mechanical energy and to electric energy. Hydrocarbons and sulphur are believed to be the only naturally occurring materials from which energy can be harnessed by combustion. Combustion of hydrocarbons is accompanied by the emission of carbon dioxide (CO2) which, until recently, was thought to be harmless but has subsequently been found to have a major deleterious effect on global warming. Combustion of sulphur produces sulphur dioxide (SO2). SO2 dissolves in water vapor to form acid, and interacts with other gases and particles in the air to form sulfates and other products that are harmful to people and the environment.
A method and system for sulphur combustion without sulphur oxides impediments is provided. This method of harnessing energy from sulphur combustion is due to the reduction of sulphur dioxide by carbonyl sulphide to sulphur vapor (S2) and carbon dioxide (CO2). In one main implementation of this technology, the entire carbon dioxide generated through this reduction reaction of sulphur dioxide is recycled to regenerate carbonyl sulphide, thus providing a zero-carbon emission combustion method and system. In terms of material balance, the mass equivalent of sulphur, oxygen and hydrogen sulphide that enter the system are removed from the system in the form of recovered elemental sulphur and water.
In general, and as will be elaborated below, sulphur is evaporated by the reaction of oxygen with liquid sulphur that is maintained in the region of its auto-ignition temperature which is about 260° C. Oxygen and liquid sulphur immediately react to form sulphur dioxide but, because the liquid sulphur is heated continuously by the combustion reaction, substantial amounts of sulphur are vaporized into the sulphur dioxide containing gas leaving the liquid sulphur:
S8 liquid(260° C.)+O2 gas→SO2 gas+heat+3S2 vapor (1)
Subsequently, the thermodynamic energy contained in the sulphur vapor (S2) is converted into heat energy through stoichiometric (or near-stoichiometric) interaction with oxygen:
S2+2O2→2SO2+heat (2)
Because of the chain character of the burning process, the sulphur vapor (S2) burns in oxygen in tenths of a second attaining a temperature level close to the theoretical adiabatic temperature of about 3000-3500° C. This high temperature is the key element of the process as it provides a major pathway for complete reduction of sulphur dioxide by carbonyl sulphide (COS) to carbon dioxide and sulphur vapor according to overall equation (3):
SO2+2COS→2CO2+3/2S2 (3)
The carbonyl sulphide (COS) can be generated by chemical reaction between a supply of hydrogen sulphide (H2S) flowing into the system and a supply of recycled carbon dioxide in which the H2S is converted to COS and water (H2O):
H2S+CO2→COS+H2O (4)
As depicted in
In one embodiment, the sulphur is evaporated by bubbling oxygen through molten sulphur at a temperature at which the sulphur boils, which ensures maximum evaporation of the sulphur. Oxygen is introduced into the bubbling chamber by line 11, is sparged through the molten bed of sulphur. The oxygen comprises substantially pure oxygen as the only gas. The pool of liquid sulphur is maintained above its auto-ignition temperature so that oxygen injected beneath the surface of this pool bubbles through the molten sulphur. As a result, sulphur vapor and sulphur dioxide are produced, the sulphur vapor being extremely useful as it can be combusted with oxygen to generate extremely high temperatures.
The composition of the vapor-gas mixture, as it flows from the bubbling chamber 90, is determined by the process parameters, such as pressure, temperature, and heat loss. The sulphur vapor may comprise diatomic sulfur gas or a combination of various sulfur species. In the method described, the heat of the reaction in the bubbling zone of the furnace is consumed to evaporate sulphur, and to heat the melt to working temperature.
As is shown in
S2+2O2→2SO2+heat (2)
Because of the chain character of the burning process, sulphur vapor burns in oxygen in tenths of a second, attaining a temperature level close to the adiabatic temperature of about 3000-3500° C. To achieve the desired chemical composition and temperature for the fluid egressing from the combustor/reactor, the sulphur dioxide gas is mixed with a predetermined amount of carbonyl sulphide that is carried into the combustor/reactor 20 through conduit 71. The carbonyl sulphide predominates in relation to the volume of sulphur dioxide that has to be entirely reduced to carbon dioxide and sulphur vapor (3), and to desirable ranges of the temperature:
SO2+2COS→2CO2+3/2S2 (3)
To give insight into how fast the reaction between COS, SO2 can occur, and how the various reaction products evolve as a function of reaction time the computation of chemical equilibrium composition was carried out using free energy minimization software over a range of temperature (700-2000K), pressure (1-35 atm), and COS:SO2 ratio (0.6:1 to 2.4:1). The reaction between COS and SO2 was simulated in COMSOL Reaction Engineering Laboratory software using the Leeds Sulphur Mechanism Version 5.2 [Sulphur Mechanism v5.2 available from http://www.chem.leeds.ac.uk/Combustion/sox.htm].
It was observed from the simulation results that the reaction between COS and SO2 at high temperature is extremely rapid and that a majority of the reaction is complete within the first 100 milliseconds. Consistent with the equilibrium predictions, the most significant species of the reaction are CO2, S2 and CO. The kinetic simulations also show that the reaction product distribution expectedly varies with time. However, an important insight gained from the simulation results is that, at a very early stage (<<100 ms), the primary product of the reaction is CO and S2 but, at longer times, the formation of CO2 occurs seemingly at the cost of CO consumption. The implication of this insight is that that the reaction product composition can, in principle, be controlled to comprise primarily CO and S2 by controlling reaction times or by an increase in carbon dioxide concentration during interaction of these gases. Therefore, this technology has potential to be used to produce carbon monoxide. If such reaction conditions are realized, the resulting reaction product would be favorable for re-association of CO and sulphur to yield COS in the lower temperature process units, if desired.
After a reduction reaction in the combustor/reactor 20 at stage II, the sulphur vapor (S2) and CO2 gas are cooled down in a heat-recovery/condenser 60 at stage VI where the sulphur is condensed (back to liquid form) and recycled through line 66 and its excess (in the form of elemental sulphur) removed (recovered) from the system 10 through conduit 63.
The carbonyl sulphide may be partially regenerated by recombination of carbon monoxide and diatomic sulphur at some point in the overall process and the recombination is favored to occur during the cooling of exhaust but primarily will be regenerated by the interaction between recycled carbon dioxide and hydrogen sulphide flowing into the system according to the following equation:
H2S+CO2COS+H2O (4)
Formation of carbonyl sulphide according to reaction (1) can be conducted in either the liquid or vapor phase. The details are published at the Transcripts of the Faraday Society, M. M. Sharms, 61 (508), page 681 (1965) and Journal of Catalysis, Akimoto and Dalla Lana, 62, 84 (1980) which is incorporated herein by reference.
Interestingly, due to the natural gas dehydration process the adsorbents used will, through the removal of the water in the gas stream, tend to drive the reaction toward the formation of COS. This is particularly the case with molecular sieves, which are the strongest dehydration agent. The phenomenon has been identified as the simultaneous H2S adsorption and rate-limited catalytic reaction of H2S and CO2 to form carbonyl sulphide and water.
The carbonyl sulfide can be formed in the system 10, from the hydrogen sulfide and carbon dioxide in a dryer (or multiple dryers) 70 at stage VII comprising a desiccant (e.g. a molecular sieve tower and/or alumina desiccants) and configured to receive a feed gas comprising hydrogen sulfide and carbon dioxide entering through lines 72 and 64, respectively, wherein the desiccant has sufficient water affinity to convert the hydrogen sulfide to carbonyl sulfide. All known desiccants are considered suitable for use herein. For example, contemplated desiccants include molecular sieves and/or alumina desiccants. The desiccant may be coated with a COS hydrolysis catalyst (e.g., gamma alumina coated with an alkali metal oxide). As COS hydrolysis is an equilibrium process (4), and it should be recognized that by continuous removal of water from a hydrogen sulfide-containing gas in the desiccant bed, the reaction shifts from COS hydrolysis towards the production of COS and additional water (which is removed by the desiccant). Therefore, under some conditions, the hydrogen sulfide in the gas is converted to COS under concomitant removal of water, and the resulting dried gas will then predominantly include COS.
The most efficient way of utilizing heat for power production is to expand the hot reaction products of the above-described process to directly produce work in a turbine expander and then to recover the remaining heat of the gas turbine exhaust gas by producing steam for driving a steam turbine.
In the pressure-exchange devices, the hot gases generated in the combustor at temperatures above the tolerance of available gas turbines are used to compress another gas in an ejector. They are cooled thereby to a level acceptable for use in present-day turbines by a flow-induction process which produces compression work on another gas. From the view point of the second law of thermodynamics, the straight cooling of combustion gases from the combustion temperature to a temperature that is acceptable for turbine operation, as practiced in conventional systems, destroys completely the energy contained between these two temperatures. Here, the same cooling is accomplished with concomitant production of useful work. The ejector, as opposed to the turbines, can operate at very high temperatures because of its inherently simple construction which results in very low mechanical stress and high reliability. However, the nature and physical conditions of the driving (primary) and entrained (secondary) fluids determine the overall conventional steady-flow ejector performance which, in general, is much poorer than that of mechanical compressors such as centrifugal or axial types. One of the main reasons for the modest efficiency of conventional steady-flow ejector-powered processes is the comparatively large mass flow ratio between the entrained and entraining fluids. The efficiency of the energy transfer can be significantly increased with the higher molecular weight ratio. Therefore, prior art conceptual applications proposed working fluids that included helium as the secondary fluid and sodium or liquid metal as the primary fluid. This was difficult to implement, however.
In an ejector, momentum can be imparted from the primary fluid to the secondary fluid by two mechanisms: the shear stresses at the tangential interfaces between the primary and secondary fluids as a result of turbulence and viscosity; and, the work of interface pressure forces acting across normal interfaces separating the primary and secondary fluids. The latter mechanism is called pressure exchange. Pressure exchange is available only in a non-steady flow field. Utilizing the reversible work of pressure forces acting at fluid interfaces between primary flow and secondary flow, a pressure exchange ejector has the potential for much greater momentum transfer efficiency than that of a conventional ejector that relies on dissipative turbulent mixing.
Garris in U.S. Pat. No. 6,438,494 disclosed a novel pressure-exchange compressor-expander, whereby a higher-energy primary fluid compresses a lower-energy secondary fluid through direct fluid-fluid momentum exchange. The pressure-exchange compressor-expander utilizes non-steady flow principles and supersonic flow principles to obtain an ejector-compressor which can attain high adiabatic efficiencies while having a simple design, small size, low weight, and which is simple and is inexpensive to manufacture.
As an example, the combustion of sulfur is integrated with combined-cycle gas and steam turbine systems. These processes do not require an excessive supply of sulfur as a feedstock because the sulfur is recycled, and it employs abundant or relatively inexpensive-to-produce hydrogen sulphide.
The combined-cycle system 10 comprises nine main stages (I, II, III, IV, V, VI, VII, VIII, IX) each having at least one unit to assist in the process of generating energy. As is illustrated in this embodiment, the Brayton cycle of the system 10 comprises a compressor 10 at stage I, a combustor 20 at stage II, an ejector 30 at stage III, and a gas turbine 40 at stage IV.
The Rankine-cycle of the system 10 comprises a heat-recovery steam generator (HRSG) 50 and a steam turbine 55 both at stage V. The system 10 comprises also of sulphur condenser(s) 60 at stage VI, molecular sieve tower(s) 70 at stage VII, an oxygen source 80 at stage VIII, and bubbling chamber (i.e. the submerged sulphur combustion furnace) 90 at stage IX, which all cooperate to constitute a system for generating electrical energy. In one embodiment, stages II and III are combined into a single device such as a pressure-exchange ejector in which both combustion and pressure exchange can occur.
In one embodiment, the sulphur is evaporated and the sulphur vapor oxidized under pressure, e.g., from about 10 to 35 atmospheres. In one embodiment, the working fluid that is to be expanded in the gas turbine 30 at stage III is obtained by steps which comprise evaporating sulphur by bubbling oxygen through the molten sulphur in the submerged-combustion furnace 90 at stage IX, oxidizing the sulphur vapor by oxygen in the combustor 20 at stage II, and then mixing the product of the oxidation with carbonyl sulphide through the pressure-exchange ejector 30 at stage III.
The oxygen-containing gas entering the system 10 (which is composed of oxygen preferably as high as 100 percent) and is obtained from an air separation unit 80 is delivered to the compressor 10 through line 82. The compressed oxygen is directed through line 11 into the sulphur bubbling chamber 90 in stage IX.
The molten sulphur is delivered into a bubbling chamber (i.e. the submerged combustion furnace) 90 at stage IX through a line 66. Mukhlenov at al., at GB 1560524 (1980), which is incorporated herein by reference, discloses a method of preparing sulphur dioxide where sulphur is evaporated by bubbling oxygen through the molten sulphur and the sulphur vapor oxidized under a pressure of 1 to 35 atmospheres.
As is shown in
To achieve the desired chemical composition and temperature for the fluid exiting from the combustor 20 at stage II to the ejector 30 at stage III the sulphur dioxide gas is mixed with a predetermined amount of carbonyl sulphide that is carried into the ejector 30 through conduit 71. The carbonyl sulphide is a gas stream of a much lower temperature than the temperature of the sulphur dioxide generated at the combustor 20. The carbonyl sulphide predominates in relation to the volume of sulphur dioxide that has to be entirely reduced to carbon dioxide and sulphur vapor (as per equation 3), and to desirable ranges of the temperature of 1,350° C. to 1,540° C. (currently the metallurgical limits for turbine inlet temperatures).
Carrying out the stage IX of submerged sulphur combustion under pressure makes it possible to utilize the energy of the gas for circulation of the gas mixture in the system. The use of an ejector transfers the energy produced during combustion to a working fluid mixture at much lower temperature, thus overcoming the challenge of handling excessive combustion temperatures in a turbine. The temperature rise of one gas equals the temperature drop in the other gas, regardless of the terminal temperature difference. The heat capacities of the two fluid streams are thus equal or the product of mass flow rate and average specific heat for the two fluid streams is equal. Since a great part of the heat is utilized in the process, this results in the generation of a high-energy gas stream comprising predominantly sulphur vapor and carbon dioxide.
Downstream of the ejector, the hot pressurized working fluid (sulphur vapor and carbon dioxide) is led by line 31 into the turbine 40 at stage IV, where the working fluid expands. Finally, the hot mixture of sulphur vapor and sulphur dioxide gas leaves the gas turbine via the exhaust 41 at temperatures up to 640° C. and directed to the heat-recovery steam generator (HRSG) 50 where the waste heat from the exhaust of gas turbines is utilized to generate steam for the steam turbine 55 both at stage V. In one embodiment, the sulphur vapor portion of the gas turbine effluent is separated from sulphur dioxide by condensation in a device that can serve as a heat recovery steam generator (HRSG) and as a condenser at the same time. As will be appreciated, more than one heat recovery and condensation unit can be provided to accomplish the cooling and condensation of the gases.
A method of sulphur condensation is disclosed by Schendel in U.S. Pat. No. 5,204,082 which is incorporated herein by reference.
This new technology is further described with reference to the following illustrative mass and energy balance calculations for the system 10 that is adapted for power generation. These energy balances are presented in
Two sets of simulations were performed at each 10 and 30 atm of upstream operating conditions. The ejector was simulated as a plug flow reactor (PFR). The PFR assumption is an idealized representation of flow in a tubular reactor wherein no radial gradients exist although the concentration, and consequently the reaction rates, can vary along the reactor length. The assumption that the ejector behaves likes a plug flow reactor is not based on any detailed insight on the fluid dynamics of the ejector.
In the first set (
It is possible that chemical reaction equilibrium may not be achieved in the condensers the heat-exchanging HRSG or even in the turbine. To assess the energy that would be recovered if the reacting gas were not equilibrated in any of the process units downstream, a second simulation was completed wherein the gas turbine (40), HRSG (50), Condenser-1 (60), and Condenser-2 (65) were modeled as process units wherein no reactions occurred although heat exchange and phase change were allowed. The results are presented in
It may be expected that the chemical composition of gas streams exiting HRSG, Condenser-1 and Condenser-2 may not be equilibrated and, accordingly, the energy requirements for an actual system would be somewhere in between the values depicted in
It can be noted that the net energy outputs for the two cases (
This novel technology also provides an alternative method for the treatment of hydrogen sulphide.
The illustrated system 10 comprises four main stages (II, VI, VII, IX,) each having at least one unit to assist in the process of generating thermal energy and sulphur recovery. Moreover, the illustrated system 10 comprises a combustor/reactor 20 at stage II, a heat-recovery/sulphur condenser 60 at stage VI, a molecular sieve tower(s) 70 at stage VII, and sulphur-submerged combustion furnace 90 at stage IX, which all cooperate to constitute a system for recovery of sulphur and for generating thermal energy while minimizing or eliminating harmful emissions to the environment.
Another embodiment of the system 10 is shown in
Sulphur recovered from natural gas has been the major source of elemental sulphur, but sulphur recovered from crude oil, either at refineries, or other processing plants, has been the fastest-growing source. For example, in Canada, such involuntary production of sulphur extracted from heavy bituminous oil sands with a sulphur content of 4-5% is now ramping up rapidly. Large stockpiles of sulphur have accumulated because much of the sulphur produced is relatively inaccessible, and further exacerbated by increasing transport costs, is becoming less economical to sell. As synthetic crude oil production increases, sulphur production could rise to a potentially unmanageable volume if a method for mass transportation is not found.
Referring still to
In addition to the four specific applications articulated above, this novel technology can be used in a number of other related applications, as described below.
In accordance with another aspect of the present invention, this novel technology can also be adapted to provide a useful, emission-free method for generating carbon monoxide. The carbon monoxide can, in turn, be used in many different industrial processes and applications, such as, for example, in the production of hydrogen (H2), in the manufacture of products such as acetic acid and methanol, in the conversion of coal to petrol, in the purification of Nickel and as a component of syngas. This novel method of producing carbon monoxide without causing any harmful emissions to the environment comprises a step of interacting carbonyl sulphide (COS), sulphur dioxide (SO2), sulphur vapor (S2) and oxygen (O2) in a combustor/reactor to yield S2, carbon dioxide (CO2) and carbon monoxide (CO). The method then entails rapidly cooling the S2, CO2 and CO while condensing the S2 in order to transform the S2 into liquid sulphur (S8) and elemental sulphur (S), the S2, CO2 and CO being rapidly cooled in order to prevent CO and S2 re-associating to form COS. This rapid cooling can be performed in a heat recovery/excess sulphur condenser such as the one designated by reference numeral 60 in
From the foregoing disclosure, it should now be apparent that this technology provides a system for combusting sulphur having means (e.g. the combustor/reactor 20) for combusting and reacting sulphur dioxide sulphur vapor, oxygen gas, and carbonyl sulphide to yield hot gases comprising sulphur vapor and carbon dioxide. The system also has means for recovering heat and condensing the hot gases (e.g. heat recovery and sulphur condenser 60) to yield steam, elemental sulphur, liquid sulphur and carbon dioxide. The system may include means for recycling the carbon dioxide (e.g. recycling lines 64, 65) to thereby enable generation of carbonyl sulphide using this recycled carbon dioxide. The system may further include means for generating carbonyl sulphide (e.g. COS generator 70) from a supply of hydrogen sulphide and a supply of carbon dioxide (e.g. recycled carbon dioxide). The system may further include an evaporation means (e.g. sulphur submerged combustor 90 such as a bubbling chamber) for generating sulphur dioxide and sulphur vapor from oxygen and liquid sulphur. The evaporation means can be used to supply the sulphur dioxide and sulphur vapor to the means for combusting and reacting. The combusting/reacting means may include an ejector for exchanging heat and pressure between the hot combustion gases exhausting from the combustor and a supply of carbonyl sulphide that is delivered into the ejector at a temperature and pressure much lower than a temperature and pressure of the hot combustion gases. The system may include a means for generating electric power from the steam (e.g. a steam turbine). The system may use the steam to perform work through rotary shaft power instead of generating electric power. The system may include a means for extracting elemental sulphur (e.g. Condenser 60 shown in
From the foregoing disclosure, it should also be apparent that this new technology provides a system for burning sulphur that entails a combustor/reactor for combusting/reacting sulphur dioxide (SO2), sulphur vapor (S2), carbonyl sulphide (COS) and oxygen (O2) to yield hot combustion gases comprising carbon dioxide (CO2) and sulphur vapor (S2). The system further includes an ejector disposed downstream of the combustor/reactor for reducing a temperature and pressure of the hot combustion gases by exchanging heat and pressure with a supply of carbonyl sulphide. The system further includes a carbonyl sulphide generator for generating the carbonyl sulphide supplied to the ejector. One or more heat recovery and sulphur condensation units can be provided for recovering heat from the hot combustion gases and for generating steam from the heat. A steam turbine can be provided for generating power from the steam. To achieve a zero-emission system, the carbon dioxide can be recycled. In one embodiment, the carbon dioxide is recycled from the one or more heat recovery and sulphur condensation units into the carbonyl sulphide generator (e.g. the molecular sieve tower 70 shown in
As shown in
As further depicted in
The system shown in
In each of the foregoing embodiments, it should be noted that the oxygen supplied to the sulphur submerged combustor (e.g. bubbling chamber 90) can be supplied under pressure. As shown in the example configuration shown in
Although specific embodiments of the invention have been described and illustrated, such embodiments should not to be construed in a limiting sense. Although not shown, each of the stages may comprise multiple units, for example multiple units for the compressor 10 or multiple gas turbine 50 units. Although not shown in the figures, it will be understood that ancillary elements and machinery such as pumps, intermediate valves or other modifications to the system 10 to adapt it for combusting of sulfur vapor may be used for proper operation of the embodiments shown. These ancillary elements and modifications are well understood by those skilled in the art. The units at each stage I through V of the combustion cycle of the first embodiment and in other embodiments may be appropriately scaled depending upon the operational scale and purpose of the facility implementing one or more of the aspects of the present invention.
Various modifications of form, arrangement of components, steps, details and order of operations of the embodiments illustrated, as well as other embodiments of the invention, will be apparent to persons skilled in the art upon reference to this description. It is therefore contemplated that the appended claims will cover such modifications and embodiments as fall within the true scope of the invention. In the specification including the claims, numeric ranges are inclusive of the numbers defining the range. Citation of references herein shall not be construed as an admission that such references are prior art to the present invention.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/CA08/01367 | 7/25/2008 | WO | 00 | 4/26/2010 |
| Number | Date | Country | |
|---|---|---|---|
| 60974965 | Sep 2007 | US |
