JPH0794669B2 - Low introduced gas velocity and high throughput biomass gasifier - Google Patents

Description

Description: BACKGROUND OF THE INVENTION The present invention relates to shredded bark, wood chips, sawdust, sludge, and other carbonaceous fuels, or fuels of various biomass forms, including raw materials, to moderately calorific fuels. The present invention relates to a gasifier for an entrained bed combustor, which is particularly applied to biomass for producing methane.

The process system according to the invention relates to the production of gas by using a high production gasifier that uses a hot sand circulation for process heat. As is known in the art, the exothermic combustion reaction can be separated from the endothermic gasification reaction.
The exothermic combustion reaction can occur in or near the combustor, while the endothermic gasification reaction occurs in the gasifier. This separation of endothermic and exothermic processes results in high energy density products without the nitrogen dilution present in conventional air-blown gasification systems.

The present invention preferably comprises a parallel entrained bed pyrolysis device, i.e., an endothermic reaction zone distinct from the exothermic reaction zone of a combustor, the heat from the epoch of which is absorbed by the circulation of inert particulate solids such as sand. The present invention relates to a new method of operating a gasifier for a system transferred to a reaction zone. The ability to operate gasifiers in entrainment mode with very low inlet gas rates and at very high fuel feed rates is an advance in the art and of commercial significance. The method disclosed by the present invention operates at typical introduction rates for fluidized beds, but at extraordinary production rates with fuel feed rates above and beyond what is believed possible based on current technology. To enable.

The novelty and surprises of the present invention relate particularly to the predictions of the design of conceptual biomass gasifiers operating in the conditions taught by the present invention, including existing fluidization design equations and published literature information on gas conversion rates of biomass. It can be easily confirmed by examination.

Specifically referenced and incorporated herein by Chan, R. and Kriegel, BB, "Modeling of physical and chemical processes during pyrolysis of large biomass pellets by experimental confirmation" ( American Chemical Society, Divi
sion of Fuel Chemistry Preprint, Vol.28, No.5, August 1983, pp. 330-337) and, in particular, FIGS. 2 and 3 shown therein.

The data on gas conversion rates of biomass published by Chan and Kriegel are used to estimate the residence time required to convert a substantial proportion of biomass to gas. The gas generation rate is 1500 for particles
To 1600 ° F. depends on the time of exposure to about the same heat flux used in a steady fluidized bed.

According to data published by Chan and Kriegel, gasification of wood chips should require drying, heating and pyrolysis of the wood with a residence time of about 2 to 3 minutes in the gasifier. . Heat balance calculations indicate that about 15 pounds of sand must be circulated per pound of wood to be gasified to provide heat for gasification.

With this information, the dimensions of the fluidized bed reactor for wood gasification can be specified. Determining the size of a fluidized bed using conventional methods to predict the dimensions that the fluidized bed must have to operate at high throughput of biomass taught by the present invention is a novelty and feature of the invention. Will be further clarified.

Since the wood and sand are constantly fed to the gasifier and the sand and charcoal are also withdrawn at a constant rate, the residence times of wood and sand are equal. Since the sand does not react, ie does not change in weight, the sand flow and sand retention in the reactor provide the basis for the design.

The residence time of wood and sand in a fluidized bed is Given by.

The sand retention in the bed is given by ρ _B h _B A _B , where ρ _B = sand density in the fluid state, pounds / cubic foot.

h _B = height of fluidized bed, feet.

A _B = fluid bed cross-sectional area, square feet.

The sand feed rate is given by W _S (pounds per hour) = W _SO (pounds per square foot-hour) _AB (square feet).

W _SO is the specific sand throughput, which determines the fluidized bed cross-sectional area required to achieve the total sand feed rate and is thus related to the wood velocity by the heat balance. As mentioned above, the heat balance requires about 15 pounds of sand per pound of wood. If one chooses a wood throughput which is shown to be possible according to the invention, for example W _WO = 2000 lbs / ft.hr and W _WO is the specific wood throughput, then the required 2 min to 3 min. It is possible to estimate the bed length of the fluidized bed needed to provide a residence time of minutes. The expression for the residence time for the above variables is Given by.

Therefore, W _SO = 500 lbs / sq ft · min Reasonable values for the bulk density of well-fluidized sand beds are common knowledge in the art, and some fluidization reference books have about 30 It is given in pounds / cubic feet.

Substituting the above formula approximately Shows that a bed height of 1 is required to provide the residence time required at the high biomass throughput taught by the present invention. However, it is well known to those familiar with fluidization techniques that "slacking" occurs in the case of elongated fluidized beds. The maximum fluid bed height to diameter ratio to avoid slacking is h / D = 5, preferably the ratio h / D
<2 is recommended for good fluidization.

Contrary to teachings in the prior art, the present invention is 2000 pounds per square foot per hour or even 4500 pounds per square foot per hour and is 10 inches in diameter and 0.83 feet long.
Can be gasified through a 22 foot unit. Moreover, its operation is smooth and has no sign of slacking.

The present invention is fundamentally outside the teachings and conventional wisdom of the prior art.

2. Description of Related Art Bailey US Pat. No. 3,853,498 describes a method involving separate gasification and combustion zones. In this Bailey process, both zones are conventional fluidized bed reactors. The wood throughput values published for this Bailey method typically do not exceed 120 pounds per square foot. Fluidization typically occurs with an inlet gas velocity of 1-3 feet / second to provide good fluidization. Since the Bailey method uses a conventional fluidized bed, the transfer of circulating sand is accompanied (en
It comes out of the top of the reaction tank by a straight flow from the fluidized bed to the fluidized bed rather than by trainment).

Skyer US Pat. No. 4,032,305 states “fast”
Another circulating bed gasifier for coal and coke, known as a "fluidized bed" is disclosed. The fast fluidized bed can be operated in a two-zone structure with an exothermic combustion zone and an endothermic gasification zone. Skyer states that the minimum velocity to achieve a circulating fast fluidized bed is slightly greater than 6 feet / second for particles with an average diameter of 60 microns. Skyer chose to operate with particles under 250 microns.

The present invention is typically 20-1000 microns, preferably 300
-Use 800 micron particles. Recalculating the 6 ft / sec minimum velocity recommended by Skyer on a finer basis to particles for the coarser invention, a minimum velocity of 30 ft / sec is required to achieve fast fluidized bed conditions. It is estimated that

Both entrained and fluidized gasification offer various advantages, including low capital investment, low upkeep, flexibility,
Includes ease of control and high conversion efficiency.

The purpose of the present invention is to operate in an entrained mode, but using an introduction rate that is typically characteristic of fluidized beds only, and at much higher fueling rates than would be possible with existing technology. It is possible to disclose a gasifier. One object of the present invention is 500-440
Disclosed is such a gasifier with a throughput that can approach or exceed 0 pounds per square foot.

The gasifier according to the invention operates in the entrained mode, but with lower introduced gas velocities and far higher wood throughputs than would be expected based on the knowledge of the prior art.
Despite the fact that it operates at an introduction rate that is typical of fluidized beds, the reactor operates in entrainment mode.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1A, 1B and 1C are schematic representations of a gasification system according to the prior art.

FIG. 2 is a schematic diagram of a gasification system according to the present invention combined with a typical parallel entrained bed pyrolysis system.

FIG. 3 is a graph of biomass throughput versus introduced gas velocity. This graph clearly shows the unique possibility of the present invention in the operation in the region called "region IV" corresponding to high throughput of biomass and low introduced gas velocity.

FIG. 4 is a schematic diagram of a gasifier useful in the method according to the present invention. The depicted cyclone separator can be inertially removed with the entrained solids, thus the gasifier optionally includes various modes including fast fluidization, bubbling fluidization, multi-solid fluidization, entrained solids. Can be combined with a combustor.

SUMMARY OF THE INVENTION From the unexpected discovery that the present invention is capable of gasifying biomass with a very high wood throughput despite being treated with an entrained gasifier operating at a low inlet gas velocity. Become.

For entrained operation, entrainment speeds are of varying degrees but to a number of intricately related variables including particle size, density, particle uniformity, column diameter, buffling, and bed depth. It was thought to be dependent, but came to be thought to depend mainly on the high inlet gas velocity.

Although fast fluidized beds have been found to have much higher throughput than bubbling fluidized beds, this type of fluidized bed typically required air inlet velocities in excess of 30 ft / sec. The biggest point that makes the present invention surprising is not that the Applicant has simply achieved buffling fluidization, but at low inlet velocities as low as 0.5 ft / sec in parallel entrainment bed pyrolysis processes, but Incorporation of inert solids was achieved using a wood throughput of 500 to 4000 pounds per square foot-hour.

DETAILED DESCRIPTION A gasifier according to the present invention basically has a fluidized bed of sand at the bottom of the reactor, fast enough to generate product gas sufficiently to entrain and circulate the sand and gasification charcoal. It is a reactor operated at a wood feed rate.

This gasifier is essentially a hybrid device with entrainment zones above the fluidized bed gasifier.

This gasifier has the features illustrated in FIG. In FIG. 4, the annular gasification vessel is provided with a conventional gas distribution plate near the bottom, and has openings for introducing a biomass material, circulating or recirculating an inert substance, and introducing a fluidizing gas at that position. . The reaction vessel has an outlet at or near the top and leads to a separator. The product gas is discharged from this separator and the fixings are recycled to the bottom of the gasifier, preferably via an exothermic combustor to reheat the inerts.

The biomass gasifier operates with the recycle granulate phase and at an inlet gas velocity in the range required to fluidize the sand or other recycle granulate phase. For example, for a 20x50 mesh sand, a speed of 0.8-2 ft.
Enables stable operation. Speeds of 0.5 to 7 feet / second can be used.

The biomass vaporizer operates at wood feed rates in excess of 3000 pounds per hour per square foot of reactor cross-section.
Throughput of 4400 pounds parallel feet per hour is achievable and can be higher. An inlet for wood supply and recirculating sand is located at the bottom of the reactor near the gas distributor. The vaporizer additionally has equipment for the removal of the circulating particulate phase and char by entrainment. For example, the separation of particulate phases such as sand and char from the product gas can be accomplished by conventional cyclones.

Referring now to FIG. 3, the inlet gas low speed, high throughput biomass vaporizer of the present invention, 200 or more, preferably 500 ~ 44
A biomass throughput of 00 pounds / parallel foot-hour, but operating at an inlet gas velocity of 0.5-7 feet / second.
This operating range corresponds approximately to region IV of the graph.

Region I represents conventional fluidized and entrained beds and operating parameters known in the art. In fact, such beds have a fixed biomass throughput of 2000 pounds / parallel foot-hour and a minimum inlet speed of 10-12 feet / second, an inlet speed of up to about 30 feet / second.

Region II is an example of the operating range of "fast fluid-beds". In order to achieve the bed densities required for fast fluidized beds, as low a solids circulation rate as possible is usually required. Region II contains the transport rates commonly used for vertical air transport of particulate matter. This is the typical operating range of a companion system that does not reduce wood throughput.

Area III shows the operating area of a conventional fluidized bed. Such floors do not work in companion mode. Experience with throughputs above 200 pounds / parallel foot-hour has not been obtained to date with conventional fluidized beds.

The method of operating a gasifier according to the present invention comprises introducing an inlet gas at a gas velocity of 7 feet / second or less to fluidize a high average density bed in the gasifier vessel. The high average density bed becomes a dense fluidized bed in the first spatial region due to its inlet gas. This dense fluidized bed contains a circulating first heated, relatively fine, inert, solid bed particle component.
Carbon-containing material into the first spatial region containing the dense fluidized bed
Introduced at a flow rate of 200, preferably 500 to 4400 pounds per square foot, the endothermic pyrolysis of the carbonaceous material is accomplished by a heated inert material in the circulation to produce the product gas. Continued above the dense fluidized bed, a lower density entrainment void region is formed containing entrained inert solid particles, carbon and a mixture of carbon-containing material and product gas. This entrained mixture is then withdrawn from the entrained space region of the vaporizer into a separator such as a cyclone, where the mixture of inert solid particles, carbon and carbon-containing material is separated from the product gas. Finally, at least the inert solid particles are returned to the first spatial region after first heating the inert particles through an exothermic reactor such as a combustor. To promote the exothermic reaction, it may be advantageous to send the entire entrained mixture excluding the product gas to the combustor.

In the present invention, a fluidized bed of heated sand or other relatively inert material at the lower end of the vaporizer vessel is
Form areas of relatively high density. Introduced wood or other carbon-containing material, which is lighter than sand, floats on the fluidized sand. As the wood is vaporized by the hot sand, an entrained region of sand, carbon and carbon-containing material particles is formed in the upper end of the vaporizer vessel.

The highest concentrations of transferred wood and charcoal would have been found at the top of the dense fluidization zone within the gasification vessel. The transferred hot sand circulates through the transferred wood and charcoal. As the carbon particles are pyrolyzed, they generate a gas that forms a fast zone over the fluidized bed. Despite the low gas inlet velocity below the bed, the gas velocity above the fluidized bed is high enough to actively move particles out of the bed.

By operating at low gas inlet velocities, high residence in the reaction vessel while surprisingly still retaining a high throughput of gas generating carbonaceous material to form a hyperkinetic zone above the fluidization zone Time can be achieved.

In this system, unlike the prior art, material from the top of the vessel is removed only by migration, despite the low gas inlet velocity below the bed. This is possible with a design that uses a fluidization zone on which there is a migration zone where particles are removed. Manipulating according to the parameters of the invention occurs exclusively depending on the amount of gas moving through the reaction vessel while avoiding the detrimental slow transfer that would be expected to occur with conventional fluidized beds of the prior art. Due to the gas, a partial migration occurs.

The carbonaceous material supplied to the gasifier is at least 60% of the available carbon that will pass through the gasification system once. The carbon residue is combusted in the combustor to generate heat for the pyrolysis reaction. If other fuels are used in the combustor, additional carbon is introduced into the gasifier.

The inlet air supplied to the gasifier is typically steam, combustion by-product gas, recycled product gas, nitrogen, air or any gas known in the art for obtaining specific products. The oxygen plant used in combination is not required for the gasification unit operated according to the invention.

In conventional fluidized bed designs, entrainment of particles into cyclones is considered detrimental to the implementation of the system. Loss due to entrainment should be avoided and, if not unavoidable, minimized as much as possible. That is, a typical fluidized bed is designed such that the lifted particles in the space above the bed are sufficient to settle into the vessel. This space has the height of the gasification vessel and is called the transport open height or freeboard space.

The present invention teaches a method of using entrainment for advantageous advantages to achieve high carbonaceous feedstock processing. The industrial advantage of the present invention is immediately apparent, as a higher throughput means a higher productivity with the same or smaller equipment, and a substantial reduction in equipment costs results from this technology.

In the present invention, entrained material exits the vessel near the top of the gasifier and is sent to a cyclone or other inert settling device to separate the product gas from charcoal, carbonaceous material and inert materials. .

The system of the present invention is flexible and could be combined with any type of combustor, fluidized, entrained or non-fluidized, to burn its inerts. The inert material can be heated in the passage through the exothermic reaction zone of the combustor to add heat. The inert material is understood to mean relatively inert as compared to carbonaceous material and includes sand, limestone, and other calcite and oxides such as iron oxide. Some of these "relatively inactive substances" are actually involved as reactants or catalysts,
Therefore, "relatively inert" is not used in strict or pure quality common sense such as noble gases. For example, in the gasification of coal, limestone is an effective means to trap sulfur and reduce sulfate emissions. Limestone is useful in the catalytic decomposition of tar in gasification.

The unpredictable aspects of the present invention reflect from the reality that the present invention cannot be reached by simply sending high volumes of carbonaceous material to the fluidized bed.

The prior art theoretical limitations on slugs are that operation at fluidization rates, addition or treatment of more carbonaceous material causes slugging, vibration and optimal self-destruction of the containment vessel over 2-5 excess. It teaches what happens at the L / D ratio. The prior art teaches that the present invention is irrelevant.

In the present invention, we have discovered an unexpected operational relationship between wood feed rate or throughput and inlet gas velocity. The relationship is that higher wood feed rates tend to result in higher inlet gas velocities which are acceptable. We have succeeded in combining both extremely high wood throughput and low inlet gas fast rise. Not only is this combination of low inlet gas velocity and high wood feed rate completely unpredictable from existing information, it is also unattainable with many combinations of available data.

Biomass conversion results in transporting sand / charcoal suspensions through the reactor and maintaining a sufficiently low suspension density on a gasifier location basis where hot sand from the combustor is continuously poured into the gasifier from the combustor. We proved by experiment. The behavior of this system in this manner is completely unpredictable based on the existing knowledge proven in previous calculations that explain the application of the fluidized bed design standards utilized and biomass gasification data. As has been demonstrated, assuming that the system is operated in the usual fluidized bed mode in a Bailey fashion, transporting hot goods to the fluidized bed is
It is required to overcome the head of _fb h _fb (ρ _fb is fluid bed density, h _fb is fluid bed height). Assuming that the wood residence time on the order of 3 minutes is required for drying, heating, and pyrolyzing the wood, and the hot sand / wood ratio is the value required for heating for gasification, much more than the wood feed rate of the present invention. It is simply calculated that it would be impossible to maintain the sand flow against the static pressure in the gasifier at a much lower rate. For example, 20001bs /
A typical fluidized bed density of 301 bs / ft ³ , with a wood throughput of ft ² h
h _fb of 50 _ft (experimental gasifier has a total height of only 22 _ft .) In addition, these high wood throughputs have L / D ratios (bed length to diameter) that allow fluidized beds to operate smoothly. Would require a fluidized bed with an L / D ratio well above. For example, fluidization tests predict slugging that causes severe vibrations in the fluidized bed when the fluidized bed L / D exceeds the value of 2-5 present in the particle size. Thus, those skilled in both biomass gasification and fluidized bed will find the present invention ineffective.

The apparatus described in the present invention is well simplified and simple to implement, so that when the gasifier operates at an inflow rate insufficient to entrain sand, but at a high throughput, gasification It is interesting to guess what actually happens in the device. At low inflow gas velocities it is probably reasonable to speculate that a short fluidized bed exists at the base of the gasifier. Fresh wood and hot sand from the combustor enter below the surface of the fluidization zone of the reactor. Due to the low density of wood and char, it is reasonable to anticipate a very high concentration of wood and char that floats on the surface of the fluidized bed rather than optionally circulating in the bed. However, the sand optionally circulates in the fluidizing zone, thereby transferring heat to the "floating" wood. Wood and char concentrations are highest at the top of the fluidized bed, where most of the gas evolves. This means that entrainment will occur from the top of the fluidized bed zone due to the high local gas velocity.

The finding that it is possible to maintain steady state residuals in reactors operating with low inflow gas velocities and high bio throughputs and with entrained sand and char removal is a significant advance over the prior art. Allows substantial improvement.

Example 1. A gasifier connected to a fluidized bed combustor A process research unit (PRU) was assembled. The system consists of a 10 inch ID gasifier connected to a 40 inch ID combustor. The gasifier and all connecting pipes were not refractory lined in order to reduce the start up and cool down times along with the time required to reach steady state. All parts in an industrial scale system constitute a system that operates in a fully integrated form.
Included in PRU. The gasifier, which accepts all the heat from the circulating entrained solid phase, must be maintained at a temperature sufficient to achieve the desired gasification conversion.
Made the PRU combustor extra large. Natural gas is added to help balance the large heat losses inherent in small systems.

The gasification reactor is designed to function at 1600 ° F and 5 psig. Carried sand and carbide (ch
ar) is separated from the product gas in the separator and returned to the combustor. The resulting carbide in the gasifier is consumed in the combustor to heat the sand phase. The combustor is a conventional fluidized bed designed to operate at 1900 ° F.

The as-received or partially dried wood chips are charged to the feed hopper. A bed of silica sand was placed in a conventional fluidized bed combustor and fluidized with air at a linear velocity of about 1.5 ft / -sec. After smooth fluidization was achieved, the starting natural gas burner was ignited. The burner acts as an air heater and is used to preheat the fluidized bed to a temperature sufficient to burn the carbides. This starting burner
It has a total heat input of 1 million Btu / hr. The wood feed rate is controlled by four metering screws below the wood feed hopper. These screws are transferred to another large horizontal conveyor screw and then to a vertical conveyor screw. The wood chips then fall into the gasifier.

Adjustment of gas flow or system pressure (typically 5 psig) is done remotely in the control room.

The PRU system can operate at wood feed rates of 50 to over 2500 lb / hr. Larger commercial wood systems can easily achieve much higher wood feed rates. Inner diameter (ID) when expressed in lb / ft ² -hr
The amount passing through a 1D ″ circular gasifier is 2500lb / hr,
Area amounts [(πr ²⁾ That the π ^{_(5/12) 2]} passes through the width of the cross-section of 0.545 square feet is the same as that 2500lb / hr.

The design specifications of the PRU system are as follows.

Gasifier size 10in, ID × 22ft length temperature 1600F pressure 20psia combustor type fluidized bed fuel charcoal and natural gas temperature 1900F size 40in, ID × 11ft length supply rate wood 50-2500lb / hr or (90-4600lbs / ft ² -Ht) Heating value of product 475Btu / SCF (dry standard) Heat carrier Silica sand gasification catalyst Steam or inert gas Conventional fuel (no pretreatment or dimensional subdivision) ・ Crushed bark ・ Wood chips ・ Sawdust ・ Dimension fuel ( hog fuel) 2. Another example of the possibility of operating under the condition of introducing low speed gas and high biomass product For example, it will be apparent to those skilled in the art that start-up of a gasifier coupled with a combustor will include the steps of heating and starting gasification.

A. Start-up Other fuels such as natural gas or wood are ignited in the combustor and burned at a rate sufficient to raise the combustor temperature at a rate that does not result in spalling of the ceramic liner. Then, circulation of sand is started between the gasifier and the combustor to raise the temperature of the gasifier. Air can be used as a transport gas in both the gasifier and the combustor during the heating phase. The gas velocity and wood throughput of the gasifier and combustor should be sufficient to entrain and circulate the sand between the gasifier and combustor. This would require as much as 15 feet / second in the sand particle size range used in the present invention. The combustion of the auxiliary fuel and the circulation of the heated sand are controlled by the gasifier at the desired temperature
Continue until reaching 1800 ° F.

B. Initiation of Gasification After the gasifier reaches the desired 1700 to 1800 ° F, at this point the gas feed to the gasifier is switched from air to steam and then the product gas is optionally recirculated. Start wood supply and gradually increase wood supply rate. As the wood gasifies, chars are created that are carried to the combustor and burned to replace the startup fuel. As the wood feed rate increases, the feed gas (steam or recycle product gas) to the gasifier is gradually reduced until the system operates in the gas velocity range of 7 ft / sec or less.

While particular embodiments of the present invention have been shown and described, it will be obvious to those skilled in the art that various modifications and improvements can be made without departing from the features of the invention. Therefore, the purpose of the claims is to cover all modifications and improvements that come within the spirit and scope of the invention.

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Claims (7)

[Claims] 1. A method of operating a gasifier, wherein an introduced gas is introduced at a gas velocity of 7 feet / second or less to fluidize a bed in a gasifier vessel, and the introduced gas is used to provide a first spatial region. In which the bed is formed into a fluidized bed, where the fluidized bed contains hot, relatively fine, inert, circulating solid bed particle components, and carbonaceous material into the first spatial region of the fluidized bed 500-4400 Feeding at a rate of pounds per square foot hour, endothermic pyrolysis of carbonaceous material by hot, inert, circulating particulate components to form product gases, near and above the fluidized bed Form a low average density entrained space region containing the entrained mixture of carbon, char and carbonaceous material and the product gas, and gradually transfer a part of the entrained mixture and the product gas from the entrained space region of the gasifier to the separator. And continuously withdraw, entrained mixture from the product gas Separated, heat to send inert solid particles to the exothermic reaction zone, returning at least the inert solid particles in a first spatial region, comprising the above steps method. 2. A method according to claim 1 wherein the inert solid particle component comprises particles having an average diameter of 300 to 800 microns. 3. Carbonaceous material at 3000 pounds per square foot
Introduce into the first space area of the dense fluidized bed at a speed more than the time,
The method according to claim 1. 4. The relatively inert solid particle component is selected from the group consisting of sand, limestone, metal oxides and calcite.
The method according to claim 1. 5. The method of claim 4 wherein the inert solid particle component comprises particles having an average diameter of 20 to 1000 microns. 6. The method of claim 1 wherein the entrained mixture is sent to the exothermic reaction zone of the combustor after the entrained mixture is separated from the product gas. 7. The method according to claim 1, wherein the separation of the entrained mixture from the product gas is carried out using a cyclone.