DE69327256T2 - METHOD AND DEVICE FOR HEATING LIQUID MEDIA BY MEANS OF PULSATING COMBUSTION - Google Patents

Abstract

In a fluid heating apparatus using a slagging or non-slagging pulse combustion system, a boiler (20) is in communication with a pulse combustion means (10). Boiler (20) includes a main fire tube (40) (Morrison tube) and a number of boiler tube conduits (41) for circulation of the hot gases for heating. Fluid to be heated enters boiler (20) through a fluid inlet means (30), with steam exiting through fluid outlet means (35). Fluid inlet means (30) allows water to enter the fluid treating vessel and fluid outlet means (35) allows steam to exit. Additionally, as shown, water may exit vessel (20) feeding a water jacket (17) around a portion of pulse combustor means (10) through line (31), with steam exiting jacket (17) and being routed to boiler (20) via line (36). Pulse combustor means (10) includes a valve means (12) which may be an aerodynamic valve (fluidic diode), a mechanical valve or the like, a combustion chamber (14) and one or more tailpipes or resonance tubes (16). Additionally, pulse combustor means (10) may include an air plenum (18) and a thrust augmenter.

Description

Field of invention

This invention relates to devices and methods for treating fluids, such as gases, water and other liquids, with heat using a pulse burner.

General state of the art

Based on studies indicating great potential for significantly increased coal firing in the commercial sector, the development of advanced coal combustion systems is currently being pursued.

Fluid heating systems known in the art include conventional combustion systems in conjunction with boiler arrangements. These conventional combustion systems primarily use oil or gas to provide heat to water passing through boiler systems. The heated water or steam is then conveyed to its desired application, such as space heating, turbine operation, or other.

Conventional oil and gas systems suffer from one major drawback - availability and price stability, both of which are subject to the turbulent conditions in the Middle East. On the other hand, solid domestic fuels are currently generally abundant and do not face the same concerns.

However, when using solid fuels such as coal, particularly the cheaper, lower quality, sulphur-containing coals, to supply heat to conventional fluid heating equipment such as a hot-tube boiler, a major concern is the amount of combustion-generated particulates and other contaminants that are entrained in the combustion gas stream. A particulate/contaminant-laden The heavily laden gas stream operating such systems can have a detrimental effect on the atmosphere if such particles are released into it. Although conventional devices such as cyclones can be used to remove larger solid particles from combustion gas streams, these devices generally fail to remove smaller solid particles such as fly ash from the streams. Similar problems exist with other gas streams where suspended solid particles have an origin other than combustion.

Nitrogen bound to the fuel also causes emissions of nitrogen oxide (NOx) to form in the gas stream. Techniques and processes to either reduce the generation of nitrogen oxides or to destroy or remove such contaminants from the exhaust stream are necessary to meet Clean Air Act requirements. Economically viable means of removing these contaminants from the exhaust stream before such exhaust is released into the atmosphere have not been available to date.

Various attempts have been made to overcome the above and other problems and to provide an economically viable and efficient process for treating fluids using a solid fuel. One such attempt has focused on the extreme cleaning of the coal prior to combustion to reduce coal-based impurities. The coal must be extensively cleaned in an attempt to remove ash and sulfur from the fuel prior to combustion. Generally, the micronized, highly cleaned coal is made into a slurry with cold water and then used as fuel. This approach is very expensive and imposes time delays before the coal can be used. However, it produces a sludge fuel made from coal that is essentially oily.

In summary, the effective reduction of suspended particles and other contaminants in a gas stream produced by combustion remains a major problem due to the lack of a cost-effective, efficient system for the removal of particles and contaminants. Available particulate capture/removal systems are limited by the operating conditions of the combustor. Any new system should possess a number of features such as high combustion efficiency, high sulfur capture capacity, high removal of solid fuel particles, low nitrogen oxide emissions, and high removal of alkali vapors generated by combustion of the fuel. New systems providing these features should be relatively inexpensive and should not require significant preparation or pre-cleaning of the fuel used for combustion.

Acoustic agglomeration is a process that uses high intensity sound to agglomerate submicron and micron sized particles in aerosols. This concept is a pre-treatment process to increase the mean size of entrained particles to allow high collection/separation efficiencies when using cyclones or other conventional separators. Sound waves cause relative motion between the solid particles, thus increasing their collision frequency. When the particles collide, they are likely to stick together. As an overall result of sonication, the particle size distribution in the aerosol shifts noticeably from smaller to larger sizes relatively quickly. Larger particles can be effectively filtered out of the carrying gas stream by conventional particle separation devices such as cyclones. The combination An acoustic agglomeration chamber with one or more cyclones in series provides a promising high-performance system to clean particle-laden gases, such as hot exhaust gases from pressurized combustors.

Acoustic agglomeration of small particles in hot combustion gases and other sources of fine dust-bearing effluent streams has been studied intermittently for several years. Although effective in generating larger particles (5 to 20 microns) for more effective removal by conventional equipment, the prior art acoustic agglomeration methods are generally not considered as potential abatement devices due to their high power requirements. For example, fine fly ash particles (less than 5 microns in size) have been agglomerated using high intensity sound fields at high frequencies in the range of 1,000-4,000 Hz. These higher frequencies were necessary for the detachment of the fine particles to cause collisions between them and thus agglomeration of the fine particles.

In these prior art acoustic agglomeration devices, the sound fields were generated by sirens, air horns, or electromagnetic loudspeakers. The resulting sound generation for acoustic agglomeration requires power estimated to be in the range of 790 to 3,162 W/m³s-1 (0.5 to 2 hp/1,000 cfm). This is, of course, a significant parasitic power loss, even for efficient horns and sirens, which typically have efficiencies in the range of 8 to 10%.

Furthermore, the siren and air horns require auxiliary compressors to pressurize air. Electromagnetic input devices require special designs and precautions to provide the desired reliability, availability and durability of the equipment. In addition, powerful amplifiers are required to drive such loudspeakers to deliver 160 decibels (dE) or more sound pressure.

In addition to the foregoing, the desired system performance objectives include dual fuel capability (i.e., coal as the primary fuel and premium gasoline as the secondary fuel), combustion efficiency exceeding 99%, thermal efficiency exceeding 80%, turndown of at least 3:1, dust-free and semi-automatic dry ash removal, fully automatic start-up with system purge and ignition control, emissions performance exceeding new source performance standards and approaching those provided by commercial-scale fuel oil-fired units, and reliability, safety, operability, serviceability, and operational life comparable to oil-fired units currently used for heating fluids.

The apparatus and method of the present invention overcome most, if not all, of the above-identified problems of the prior art and generally possess the desired features set forth above by using a pulse combustor to provide a heat source for enhancing the production of fluid heat, such as steam production. The present invention can be designed to operate in both a slag-forming and a non-slag-forming mode.

Summary of the invention

It is therefore an object of the present invention to provide an improved fluid heating device and method.

Another object of the present invention is to provide an improved combustor that operates on sulfur-rich fuels such as coals while providing improved heat source production and simultaneously providing efficient cleaning of particulates generated by the combustion of such fuels.

Yet another object of the present invention is to provide a high efficiency pulse combustion system for heating a fluid.

Yet another object of the present invention is to provide a means for removing undesirable contaminants from the hot gaseous stream produced by the high efficiency pulse combustor.

Another object of the present invention is to provide for the capture of contaminants and the removal of particulate combustion products entrained in a gas stream.

Another object of the present invention is to provide a pulse combustor for producing a heat source for increased steam production.

Another object of the present invention is to provide a slag forming pulse combustion system for improved heating of fluids.

Yet another object of the present invention is to provide a non-slag forming pulse combustion system for improved heating of fluids.

Yet another object of the present invention is to provide a fluid heating device that improves particle removal from a gas stream used to heat fluids.

From one aspect and starting from EP-A-0 370 504, the invention provides an apparatus for heating a fluid using a fluid heating vessel, such as a hot tube boiler, the vessel having means therein for containing a fluid to be heated and fluid inlet and outlet means in communication therewith, the vessel having means therein including a hot tube for heat exchange between hot gases passing through the heat exchange means and the fluid, outlet means from the heat exchange means being provided; and the apparatus further comprising pulse combustion means, e.g. B. square or tunable, in connection with the heat exchange means of the fluid heating vessel, the pulse combustion means being capable of combusting a fuel/air mixture to produce a pulsating stream of hot combustion products and a sound wave at a frequency in the range of 20-1,500 Hz, the pulse combustion means also comprising valve means for receiving a fuel/air mixture when required, a combustion chamber in connection with the valve means and at least one resonance tube in connection with the combustion chamber and the heat exchange means of the fluid heating vessel to supply hot gases to the heat exchange means, the apparatus further comprising means, such as a cyclone, for removing particulate matter from the gas, wherein the pulse combustion device cooperates with the heat exchange device such that the pulsating stream of hot combustion products and the sound wave supply heat and acoustic vibrations directly to the heat exchange device, and wherein a portion of the at least one resonance tube is located in the heating tube of the vessel for heat transfer therefrom to the fluid in the portion of the fluid heating vessel.

From another aspect, the invention also provides a method of heating a fluid comprising the steps of:

a) passing a fluid to be heated through a vessel;

b) pulse combustion of a fuel in a pulse combustor in communication with the vessel, the pulse combustor having at least one resonance tube, a portion of the at least one resonance tube being located in a heating tube of the vessel, the at least one tube operable to produce a pulsating stream of combustion products and an acoustic pressure wave at a frequency of about 20 to about 1,500 Hz, and the stream of combustion products and the acoustic pressure wave being directed into the vessel to thereby effect heat transfer to the fluid for a predetermined heating of the fluid;

(c) removing particulate materials from the stream of combustion products; and

d) conveying the heated fluid to perform its intended function of acting as a heat source for various heating devices.

Short description of the characters

The structure intended to implement the invention is described below together with its further features.

The invention will be more readily understood from reading the following description and with reference to the accompanying drawings forming a part hereof, in which an example of the invention is shown and in which:

Fig. 1 is a schematic representation of a boiler tube apparatus with pulse combustion for heating fluids according to the present invention,

Fig. 2 is a more detailed schematic view of the pulse combustor device of the apparatus shown in Fig. 1,

Fig. 3 is a schematic representation of a valve device for a pulse combustor for use in the present invention,

Fig. 4 is a schematic representation of a compact pulse combustor that can be used in the device according to the present invention,

Figure 5 is an illustration of a preferred pulse combustion chamber for use in an apparatus according to the present invention,

Figs. 6A and 6B are diode effect diagrams for a diffuser-based aerodynamic valve assembly for a pulse combustor for use in an apparatus according to the present invention.

Figs. 7A and 7B are illustrations of a tandem set of pulse combustors showing a fuel injector for each pulse combustor,

Fig. 8 shows another embodiment of a fluid heating device with pulse combustion according to the present invention,

Fig. 9 is a schematic representation of another preferred embodiment of a pulse combustor for use in an apparatus according to the present invention.

Description of the preferred embodiments

The preferred apparatus for heating a fluid according to the present invention integrates a pulse combustor device with a fluid treatment vessel having means for receiving a fluid to be heated and permitting entry and exit of the fluid therefrom. The fluid treatment vessel further includes means for permitting the passage of hot gases generated by a pulse combustor, the gases being in heat exchange relationship with the fluid to be heated. The apparatus further includes means for removing particles entrained in the combustion product stream generated by the pulse combustor and may additionally utilize an advanced design of the pulse combustion chamber and valve means. The pulse combustor system according to the present invention is particularly useful for burning a solid fuel such as low grade coal.

Advanced coal-fired combustors generally use coal that has been processed into one of the following forms: dry pulverized coal, dry ultrafine coal, coal/water mixture. Dry pulverized coal is conventional ground coal that typically has a product fineness of 70% through a sieve with 74 µm (200 mesh) and less than 3% surface moisture. This is the cheapest of the three forms. Dry ultrafine coal is a product of an integrated process that includes grinding, drying and beneficiation. Thus, ultrafine coal is a fine powder with low ash and sulfur content and is more expensive than dry pulverized coal. Coal/water mixture refers to a mixture of pulverized coal and water with certain chemicals added to improve stability and flow characteristics. A fuel in the form of a coal/water mixture is cheaper and safer to transport and store than dry pulverized coal and dry ultrafine coal. However, the availability of fuels in the form of a coal/water mixture is quite limited.

Pulse combustors can burn any type of coal efficiently (more than 99% carbon conversion) and without gas carriers. However, dry pulverized coal is more economical to burn and boasts more mature technology and infrastructure compared to dry ultrafine coal. The high combustion intensity and the sound wave achieved in pulse combustion allow the use of pulverized rather than ultrafine coal without any performance penalty. Furthermore, according to the present invention, sulfur and particulates are to be removed from the combustion product stream, and therefore the cheaper, unprocessed coal can be used advantageously.

When unrefined coals are used to fuel the pulse combustion system in the present invention, contained sulfur must be removed to meet emissions requirements. For this purpose, sorbents for generated sulfur derivatives can be injected into the system. Exemplary sorbents for sulfur derivatives include limestone, lime, slaked lime and dolomite. A particularly preferred sorbent for the present invention is Gen-Star limestone having a calcium carbonate content of about 89% by weight.

The present invention is particularly useful for heating water to produce steam. The ability of steam to give off heat, promote its own circulation, and allow ease of distribution and control in a heating system are equally advantageous. Moreover, a significant number of steam heating systems already exist throughout the world, representing a large, affordable market, although many such systems are fired with petroleum-based fuels which are subject to significant price instability and availability, as discussed above. It should be appreciated, however, that other fluids, such as gases or other liquids, can be heated by the apparatus disclosed herein.

An apparatus of the present invention with combustion, heat recovery and emissions control systems is shown in Figure 1. This embodiment integrates a pulse combustor with a heat recovery system via a main heat pipe with a conventional cylinder boiler 20. This particular embodiment is shown operating in a non-slagging mode. A non-slagging mode is achieved by maintaining the temperature of the system below the point at which the particles formed during combustion and the sorbents added to the combustion product stream, if any, begin to slag (become melted). Of course, in a non-slagging arrangement, solid particles must be removed from the hot gas stream.

In Fig. 1, the boiler 20 is connected to a pulse combustion device, generally 10. The boiler 20 includes a main heating tube 40 (Morrison tube) and a number of boiler tubes 41 for circulating the hot gases for heating. Although a four-pass heating tube boiler is shown, a water tube boiler could be used with obvious modifications. A fluid to be heated enters the boiler 20 through a fluid inlet means 30, with steam exiting through fluid outlet means 35. The fluid inlet and outlet means 30 and 35 may be any type of conventional connection which allows fluids to enter or exit a pressurized vessel. In the arrangement described here, the fluid inlet means 30 allows water to enter the fluid treatment vessel and the fluid outlet means 35 allows steam to exit. Additionally, as shown, water may exit vessel 20 feeding a water jacket 17 around a portion of pulse combustor 10 via line 31, with steam exiting jacket 17 and being passed to boiler 20 via line 36.

The pulse combustor 10 includes a valve device 12, which may be an aerodynamic valve (fluid diode), a mechanical valve, or the like, a combustion chamber 14, and one or more exhaust pipes or resonance pipes 16. In addition, the pulse combustor 10 may include an air chamber 18 and an axial pressure booster device (not shown).

The pulse combustor 10 of Fig. 1 is more readily seen in Fig. 2, in which like numerals represent like elements. In Fig. 2, a plurality of resonance tubes 16 extend into the main heating tube (or Morrison tube) 40. Water may be contained in the jacket of the main heating tube 40 in a conventional manner. The pulse combustor shown in Fig. 2 may also utilize flanges 62 and balance tube joints 67, if they are necessary for the connection to the boiler 20.

The resonance tubes 16 may use a number of different designs. For example, the tube may continuously flare outward (shown in the embodiment of Figure 8), allowing the entire resonance tube 16 to act as a diffuser. Such diffusion reduces the gas exit velocity from the combustion chamber 14 and provides for recirculation of combustion products and increased residence time of the particles in the pulse combustor 10. A compact pulse combustor design using a spiral resonance tube 16 is shown in Figure 4. In this embodiment, the resonance tube 16 is surrounded by a water jacket 90 so that steam generated by the heat in the resonance tube 16 can be removed from the system and directed to a boiler or other heated fluid device. In a further design, the resonance tube 16 may be substantially straight as in Fig. 1, but may have a diffuser section at its outer end consisting of an outwardly flaring exhaust pipe section. Alternatively, the resonance tube 16 may incorporate a diffuser section at the end closest to the combustion chamber 14 with a substantially straight tube extending therefrom (shown in Fig. 9).

When operated as described below, the pulse combustor device 10 produces a pulsating stream of hot combustion products with a sound wave having a frequency in the range of about 20 to about 1,500 Hz. When fuel is combusted, a pulsating stream of hot combustion products exits the combustion chamber 14 and enters the resonance tubes 16 of the pulse combustor device 10, and the tubes 16 can water jacketed or not, as the system dictates. As shown in Fig. 1, the end of the Morrison tube 40 opposite the pulse combustor assembly 10 acts as a decoupler section 50 where the stream of hot combustion products leaves the resonance tubes 16 and begins a passage through the array of conduits 21 of the boiler 20.

An ash drop chute 60 or other means may also be provided to remove a portion of the particulates in the gaseous combustion product stream. Placement of the chute in the decoupler section 50 of the Morrison tube 60 removes significant particulates from the gas stream prior to the gas's passage through the remainder of the boiler 20. A shock or inertial solids separator is one of the alternative means that may be used to effect partial removal of particulates from the gas stream. The hot combustion product stream exits the resonance tube 16 at the decoupler section 50 and then enters the line 41 to begin its passage through the boiler 20. Prior to entering the line 41, a portion of the larger particulates entrained in the combustion product stream tend to separate from the gaseous stream. These particles may then be captured and removed through the ash drop-out chute 60 as the gas stream makes its first turn in the hot gas passage means. The remaining particulate material in the gaseous stream substantially remains entrained in the gas stream as it passes through the boiler lines 41.

As previously explained, the pulse combustor 10 can operate at a temperature below the slagging point of the particles contained in the gas stream so that solids remain suspended. When operated in a non-slagging dry ash discharge mode the need for a refractory lining for the combustion chamber 14 and the resonance tubes 16 is eliminated, but a multiple resonance tube arrangement utilizing four (4) or more exhaust tubes may be necessary.

Another benefit of operating in a non-slag forming mode is the potential for reduced nitrogen oxide emissions and improved sulfur capture. Lower temperatures improve control of both of these contaminants. Additionally, multiple air stage separation can be used to further control nitrogen oxide emissions. Incorporating multiple air stage separation with near stoichiometric or sub-stoichiometric combustion in the combustion chamber 14 and exhaust pipe 16 through secondary addition of air into the decoupler section 50 also reduces nitrogen oxide emissions.

The boiler lines 41 may be arranged in the boiler 20 in a conventional serpentine pattern in the fluid to be heated. As the hot gas stream passes through the boiler 20, heat is transferred to the lines 41 surrounding the fluid. However, as previously mentioned, a water tube boiler may also be used in which the fluid to be heated is circulated through a line and in which the hot gases surround it. The heated fluid may be supplied to other applications, such as space heating.

After the hot gases have left the boiler 20, they are fed to another device for removing a substantial portion of the residual particulate material entrained therein. Conventional devices for collecting/removing particles for this purpose are designated 70 in Fig. 1. Such conventional systems for contain one or more cyclones or other solids separators. The gas from the cyclone 70 is allowed to escape to the atmosphere via an exhaust outlet. The collected fly ash and other particulate material, including any sorbent that may have been injected into the system for sorption of contaminants, is removed via the separator 70.

An induced draft fan 80 may be positioned along the hot gas passage and adjusted to preferably maintain a zero static gauge pressure in the decoupler section 50. Additionally, a forced air fan 90 may be used to supply primary air to the plenum 18. The plenum 18 operates as a capacitor and attempts to supply primary air to the pulse combustor 10 at approximately constant static pressure. The pressure gain developed due to the pulse combustion in the present apparatus also reduces the size, power requirements and cost of the forced air fan 90 and the induced draft fan 80.

As previously mentioned, a sorbent such as slaked lime, lime, limestone or dolomite may be injected into the pulse combustor 10 or anywhere along the hot gas passage when it is operated in a non-slagging mode to effect sorption of the contaminants present in the hot gaseous stream. In particular, the sorbents identified above are useful in removing sulfur derivatives such as sulfur dioxide from the gas stream.

Alternatively or in addition to the injection device for the sorbent, a device for injecting particles with a size that depends on the size of the particles in the combustion particles entrained in the product stream.

Bimodal agglomeration occurs whereby particles of different sizes are agglomerated with acoustic amplification provided by the pulse combustor 10. The pulse combustor 10 generates an intense sound wave through separation induced pressure oscillations when fired with a fuel. The combustion generated sound field resonates through the resonance tubes 16 which act directly on the gaseous stream carrying the particles to cause acoustically enhanced bimodal agglomeration of the particles in the gaseous stream. Because the agglomerates are larger, enhanced removal of the agglomerated particles is permitted either at the first bend of the hot gas passage means through the ash discharge chute 60 or at the downstream location of the removal means 70.

The particles used to enhance acoustic agglomeration and/or contaminant capture are preferably introduced into the system near the junction of the pulse combustion chamber 14 and the resonance tubes 16. The interface between the resonance tubes 16 and the combustion chamber 14 is an area of high heat release and high heat transfer. The high heat provides a rate of sorbent calcination which further provides high porosity in the calcined sorbent, which in turn produces a high surface area to mass ratio without the need for micronization of the sorbent. This, together with the effects of the oscillating flow field, enhances sorbent utilization at relatively low calcium to sulfur molar ratios on the order of about 2.5.

The design of the present apparatus can operate for the production of saturated steam at low pressures [less than 2.1 bar (30 psig) and preferably about 1.0 bar (15 psig)]. The boiler jacket used in the present invention can be one originally intended for oil and gas fired systems. Furthermore, the apparatus disclosed here has a space requirement similar to that for oil and gas fired boilers.

Other attempts to produce a clean combustion gas stream have used a slag-producing combustor concept to remove the majority of the ash particles. Coal combustors operate at a sufficiently high temperature by controlling the stoichiometry of the combustion air in an adiabatic combustion chamber to near stoichiometric so that ash is melted and removed from the exhaust gas in the form of slag.

The high temperatures at which the slag-forming combustors must operate tend to increase the amount of nitrogen oxides produced during the combustion process. This in turn generally requires additional equipment downstream of the coal combustor to reduce the concentration of nitrogen oxides in the effluent gas stream. The high combustion temperatures in the slag-forming combustors are also unsuitable for introducing a sulfur sorbent at the pulse combustor 10 because the sorbents, when added, also slag, destroying their ability to effect sorption of contaminants.

The pulse combustor device 10 may be designed for a dual fuel capacity. The primary fuel may be coal and the secondary fuel may be natural gas. The Secondary fuel not only enables rapid start-up of the unit but also provides backup in the event of an interruption in the primary fuel supply.

A pulse combustor, such as that used in the present invention, typically operates in the following manner. Fuel and air enter the combustion chamber 14 and an emission source detonates the explosive mixture during start-up. The sudden increase in volume induced by the rapid increase in temperature and evolution of combustion products pressurizes the chamber 14. As the hot gas expands, the valve means 12, preferably a fluid diode, allows preferential flow toward the resonance tube 16. The gaseous combustion product stream exiting the combustion chamber 14 and resonance tube 16 has significant momentum. Due to the inertia of the gases in the resonance tube 16, a vacuum is created in the combustion chamber 14. The inertia of the gases in the resonance tube 16 allows only a small fraction of the exhaust gases to return to the combustion chamber 14, with the remainder of the gas exiting via the resonance tube 16. Because the chamber pressure is below atmospheric pressure, air and fuel mixtures are drawn into the chamber 14 where auto-ignition takes place. The valve means 12 again limits backflow and the cycle begins again. Once the first cycle is initiated, the engine operation is self-sustaining thereafter.

The valve device used in many pulse combustion systems is a mechanical "flapper valve". The flap valve is actually a check valve that allows flow from the inlet to the combustion chamber and reverse flow through a mechanical seat arrangement. Although such a mechanical valve can be used in conjunction with the present system, an aerodynamic valve with no moving parts is preferred. With an aerodynamic valve, a boundary layer forms in the valve during the exhaust stroke and turbulent vortices throttle much of the reverse flow. In addition, the exhaust gases are at a much higher temperature than the supply gases. Consequently, the viscosity of the gas is much higher and the reverse resistance of the inlet diameter is in turn much higher than that for forward flow through the same opening. This phenomenon combines with the high inertia of the outgoing gases in the resonance tube 16 to give a preferential and average flow from inlet to outlet. Thus, pulse combustion creates a self-aspirating engine which draws its own air and fuel into the combustion chamber 14 and self-ignites combustion products.

The preferred pulse combustor used here for a coal fired system is based on a Helmholtz configuration with an aerodynamic valve. The pressure fluctuations caused by combustion in the combustor shaped like a Helmholtz resonator, combined with the fluidic diodicity of the aerodynamic valve, cause a bias flow of air and combustion products from the inlet of the combustor to the outlet of the resonance tube 16. This results in the combustion air being self-aspirated by the combustor and an average pressure increase developing in the combustion chamber to expel the combustion products at a high average flow rate (over 1,000 feet/second) through the resonance tube 16.

The generation of an intense sound wave is a characteristic of pulse combustion. The sound intensity after the wall of the pulse combustion chamber 14 is often in the range of 110 to 190 dB, which can be varied depending on the desired sound field frequency to suit the specific application undertaken by the pulse combustor.

The rapid pressure variation across the combustion chamber 14 creates the strong oscillating flow field. In the case of coal combustion, the oscillating flow field causes the combustion products to be swept away from the reacting solid coal, providing access to oxygen with little or no limitation to diffusion. Second, pulse combustors experience very high mass transport and heat transport rates in the combustion zone. While these combustors tend to have very high heat rejection rates (typically ten times that of conventional combustors), the high mass transport and heat transport in the combustion zone result in a more uniform temperature. Thus, the peak temperatures achieved are much lower than in the case of conventional systems. This results in a significant reduction in the formation of nitrogen oxides (NOx), as previously noted. The high heat release rates also result in a smaller required combustor size for a given firing rate and a reduction in the required resonance time.

In some particular embodiments of the present invention, a pulse combustion chamber design of the type shown in Figure 5 is preferred. This design uses square-shaped generators to define an axisymmetric geometry that would be similar to accommodate a number of design and chamber performance characteristics. The alphanumeric legends on the pulse combustor shown in Figure 5 correspond to the following dimensions, which relate to a slag-forming combustor design (as described below): with a heat output of 2,200 kW (7.5 MMBtu/h) and can be used to determine other pulse combustor designs. The inlet port 100 has a diameter of 14.4 cm (5.69 inches) and the outlet port 101 has a diameter of 12.8 cm (5.06 inches). The lengths of the various sections of the combustion chamber are as follows: L₁ is 41.1 cm (16.17 inches), L₂ is 10.5 cm (4.15 inches), L₃ is 10.9 cm (4.31 inches), L₃ is 8.6 cm (3.40 inches) with a combined length of the combustion chamber from the inlet port 100 to the outlet port 101 of 71.2 cm (28.03 inches). The angle α is 40º, the length R1 is 63.9 cm (25.15 inch), the length R2 is 16.4 cm (6.46 inch), the length R3 is 10.9 cm (4.31 inch), and the length R4 is 8.6 cm (3.40 inch).

The pulse combustor systems of the present invention regulate their own stoichiometry within their firing region without the need for extensive controls to regulate the mass flow ratio of fuel feed to combustion air. As the fuel feed rate is increased, the magnitude of the pressure pulsations in the combustion chamber 14 increases, which in turn increases the amount of air drawn through the aerodynamic valve. Thus, the combustor automatically maintains a substantially constant stoichiometry over its particular firing region. The induced stoichiometry can be changed by modifying the fluid diode of the aerodynamic valve.

The aerovalve as shown in Fig. 3 can also be used in the present invention so that the acoustic pressure wave of the pulse combustor is adjustable. As shown schematically, a fixed sleeve is in communication with the combustion chamber 14 with the aerovalve 12 mounted therein for reciprocating movement therealong. The valve 12 is in turn connected to a control device, such as a linear actuator 48, which imparts the desired movement to the valve 12. For example, movement of the valve 12 modifies the fuel residence time in the combustion chamber supply as well as the stoichiometry. If the valve 12 is closer to the chamber 14, less residence time is available. Increased residence time allows for better fuel/air mixing as well as greater removal of fuel volatiles. Likewise, while a fuel/air mixture may be introduced via an inlet line 45 extending through the chamber 18, an injection point 47 for the sorbent therealong may be used, providing axial adjustment such as by a linear actuator 49.

A further illustration of the diode effect of the chamber inlet and outlet diffusers using the features of the diffuser-based aerodynamic valve design is shown in Figures 6A and 6B. In this design, two simple, opposing tapered diffuser sections comprise the aerodynamic valve. A steep diffuser angle is used at the inlet, which can be between 40º and 60º (half cone angle). On the combustion chamber side, a diffuser with a sufficiently shallow angle is used to provide efficient pressure recovery (4º to 7º). The length of the diffuser sections and the minimum diameter of the aerodynamic valve are selected to meet the combustor integration and performance requirements. These variables can change the total fluid diodericity and the minimum refeed resistance for a given average flow rate.

The characteristics of the air intake flow are shown in Fig. 6A. The boundary layer formation, which is monotonic in the direction of flow, is compensated by the diverging cross-sectional area of the flat diffuser section. The intake flow also draws from a large area near the valve inlet since there is no flow separation at the inlet from the steep diffuser due to the flow acceleration from a wide to a narrow cross section.

The exhaust flow characteristics are shown in Fig. 6B. The boundary layer formation along the length of the shallow angle diffuser in the direction of flow, together with the diffuser angle, causes the minimum effective diameter to be small. The flow is then separated by the steep angle diffuser with reverse flow, causing the streamlines to remain in a small cross-sectional area for the exhaust.

Both flow characteristics and differences in temperature between the intake air and the chamber return gases give rise to the fluidicity of the aerodynamic valve. With the fluctuating pressure in the chamber, the fluidicity of the aerodynamic valve causes the net flow at the aerodynamic valve to receive combustion air at a self-induced stoichiometry level.

In some embodiments of the present invention, two (2) pulse combustors may be arranged in a tandem configuration where the combustion chambers and exhaust pipes form a common heater pipe (not shown). Tandem operation uses a 180º phase delay between each combustor unit and results in superposition of sound waves and cancellation of volatile sound emissions. A tandem configuration also provides for automatic fuel synchronization and pre-combustion. seal. However, in some tandem designs, the amount of fuel injected forcefully into the pulse combustor during the exhaust phase is reduced. Such injection can be undesirable because fuel particles are expelled from the pulse combustion chamber quickly and prematurely, resulting in low combustion efficiency.

An alternative embodiment using tandem combustors which more effectively reduces injection of fuel during the exhaust phase and is preferred is shown in Figs. 7A and 7B. In this tandem configuration, fuel is supplied along a tee 150 of the main fuel line, with one leg of the tee connected to each of the tandem combustors. The fuel tee 150 acts as a connection allowing automatic fuel preloading between the pulse combustor chambers 160 and 170. Efficient synchronization of the fuel in the fuel tee 150 is accomplished by the ability to operate the pulse combustor chambers 150 and 160 in tandem 180° out of phase. Under these conditions, one combustion chamber reaches a low pressure phase just as the other chamber simultaneously reaches a high pressure phase. Due to the pressure gradient present in the fuel connecting tee 150, combustion products are accelerated from the high pressure chamber to the low pressure chamber. The momentum of the accelerated gases pre-stresses a fuel flow from the main fuel source into the fuel line tee 150 and finally into the low pressure combustion chamber. Half a cycle later, a similar phenomenon occurs in the opposite direction. This allows fuel to be properly synchronized without the use of mechanical flap valves or an independent synchronization chamber. The natural instability of the tandem units, which requires a using a common fuel interconnection line is sufficient to automatically put the two combustion units 180º out of phase because the units inherently seek the most stable and least sensitive operating condition. This condition results in efficient fuel synchronization, ie a 180º phase delay.

There are various means for connecting tandem combustion units 150 and 160, including an exhaust pipe connection or an aerodynamic valve connection. The exhaust pipe connection is an effective approach due to the pre-compression effect of the high momentum exhaust fluids which allow unburned particles to be retained within the influence of the strong, fluctuating flow field of the combustion products at the exhaust region for a longer period of time.

The apparatus of the present invention can also be arranged to operate in a slagging mode in which the temperature of the system is at least that required to slag the particles in the gas stream. A design for a slagging combustor according to the present invention is shown in Figure 8, in which like numerals represent like elements discussed with reference to Figure 1. A slag discharge valve 310 is kept hot with an auxiliary burner so that the slag remains molten and flows into a slag collection vessel without clogging the collection opening.

The resonance tube 16 and the water-cooled decoupling section 300 are designed in a U-shape in Fig. 8 to accommodate the requirements of the limited space. For slag forming operations, a combustion chamber 14 and a resonance tube 16 with refractory lining can be used. be required. A slag discharge valve 310 is provided at the bottom of the decoupler 300 and may be of any type of outlet capable of removing slag from the system. As shown, slag generally forms on the interior walls of the resonance tube 16 and the decoupler section 300 and drains to the slag discharge valve 310 where it remains heated for removal in a conventional manner.

Fig. 8 also shows the previously mentioned axial pressure amplifying device 19 in connection with the valve device 12 and contained in the air chamber 18.

When operating in the slag forming mode, a means for introducing a sorbent for capturing contaminants should be provided downstream of the pulse combustor means 10. The low temperatures downstream allow the sorbent to remain in solid form, thereby allowing the sorbent to adequately carry out sorption of the contaminants. As shown in Figure 8, such a means for introducing the sorbent is shown downstream of the decoupler section 300 at inlet 330. The means for introducing the sorbent may comprise any conventional opening that allows introduction of particles into a pressurized chamber.

In addition to the cyclone 70, a scrubber unit 360 is shown for further cleaning the particles from the gas stream before the gas is discharged into the atmosphere.

Another embodiment of the pulse combustor device 10 which can be used in this invention, showing additional features thereof, is shown in Fig. 9. In particular, Fig. 9 shows the resonance tube 16 water cooled with a water jacket therearound. In addition, Fig. 9 shows the previously described configuration of the resonance tube 16 in which the resonance tube 16 flares outward immediately from the combustion chamber 14 but then straightens outward thereafter. In this embodiment, the length A is 35.9 cm (14.15 inches), the length B is 91.4 cm (36.00 inches), and the length C is 194.7 cm (76.67 inches).

Claims (13)

1. An apparatus for heating a fluid utilizing a fluid heating vessel (20), such as a hot tube boiler, the vessel having means therein for receiving a fluid to be heated and fluid inlet and outlet means (30, 35) in communication therewith, the vessel (20) having means (40, 41) therein including a hot tube (40) for heat exchange between hot gases passing through the heat exchange means (40, 41) and the fluid, outlet means from the heat exchange means (40, 41) being provided; and the apparatus further comprising pulse combustion means (10), e.g. B. square or tunable, in connection with the heat exchange device (40, 41) of the fluid heating vessel (20), the pulse combustion device (10) being capable of combusting a fuel/air mixture to produce a pulsating stream of hot combustion products and a sound wave at a frequency in the range of 20-1,500 Hz, the pulse combustion device (10) also including valve means (12) for receiving a fuel/air mixture when required, a combustion chamber (14) in connection with the valve means (12) and at least one resonance tube (16) in connection with the combustion chamber (14) and the heat exchange device (40, 41) of the fluid heating vessel to supply hot gases to the heat exchange device (40, 41), the device further including means, such as a cyclone (70), for removing particulate matter from the gas, the pulse combustion device (10) cooperates with the heat exchange device (40, 41) so that the pulsating flow of hot combustion products and the sound wave supply heat and acoustic vibrations directly to the heat exchange device (40, 41) and wherein a portion of the at least one resonance tube (16) is located in the heating tube (40) of the vessel (20) for heat transfer therefrom to the fluid in the portion of the fluid heating vessel (20). 2. Device according to claim 1, wherein the device can be operated at a pressure of 1 to less than 2.1 bar. 3. Device according to claim 1, in which a section of the pulse combustion device (10) and the at least one resonance tube (16) of the pulse combustion device (10) are jacketed (17, 90) for water cooling. 4. Apparatus according to claim 1, wherein the means for removing particulate material is located downstream of the fluid heating vessel (20). 5. Apparatus according to claim 4, further comprising means (60) disposed along an initial portion of the heat exchange means (40, 41) for partially removing particles from the gas passing therethrough. 6. Apparatus according to claim 5, wherein the heat exchange means (40, 41) comprises at least one tube (41) extending through the vessel (20) along a serpentine path forming a plurality of passages back and forth through the vessel, and wherein the means (60) for partially removing particles is located upstream of a point where the tube reverses its path in the vessel. 7. Apparatus according to claim 1, wherein the fuel valve device (12) of the pulse combustion device (10) can be adjusted back and forth with respect to the combustion chamber (14). 8. A method for heating a fluid comprising the steps : a) passing a fluid to be heated through a vessel (20); b) pulse combustion of a fuel in a pulse combustor (10) in communication with the vessel (20), the pulse combustor (10) having at least one resonance tube (16), a portion of the at least one resonance tube (16) being located in a heating tube (40) of the vessel (20), the at least one tube (16) operable to produce a pulsating stream of combustion products and an acoustic pressure wave at a frequency of about 20 to about 1,500 Hz, and the stream of combustion products and the acoustic pressure wave being directed into the vessel (20) to thereby effect heat transfer to the fluid in the vessel (20) for a predetermined heating of the fluid; (c) removing particulate materials from the combustion product stream; and d) conveying the heated fluid to perform its intended function of acting as a heat source for various heating devices. 9. Method according to claim 8, in which the pulse combustion device (10) is operated at a temperature below the slagging point of the combustion products of the fuel burned therein. 10. A method according to claim 8, wherein the pressure in the vessel in which the fluid is heated is maintained at a level below 2.1 bar. 11. The method of claim 8 further comprising the step of introducing a particulate material having a size distribution different from the particulate material resulting from the pulse combustion into the stream of combustion products to cause bimodal agglomeration of the particulate material, optionally wherein the introduced particulate material is a sorbent for contaminants in the combustion product stream. 12. A process according to claim 11, wherein the contaminant is a sulfur product and the particulate material is a sorbent therefor. 13. A method according to claim 8, including a step of partially removing agglomerated particulate material from the stream of combustion products before the stream leaves the vessel (20).