WO1981001713A1

WO1981001713A1 - Fluidized-bed process to convert solid wastes to clean energy

Info

Publication number: WO1981001713A1
Application number: PCT/US1980/001657
Authority: WO
Inventors: R Davis; H Kosstrin; D Himmelblau
Original assignee: Energy Resources Co Inc
Priority date: 1979-12-14
Filing date: 1980-12-15
Publication date: 1981-06-25
Also published as: ZA807805B; NL8020492A; BR8008928A; SE8104818L; GB2075543A; FR2473913A1; JPS56501764A; CA1160104A

Abstract

A method to pyrolyze biomass materials such as rice hulls, municipal waste, etc., to produce useful oil, gas, and char. Disposal of biomass waste materials by burning in boilers results in coating of parts by molten ash, and air pollution. The invention provides for disposal of biomass materials by conversion to oil, gas, and char by pyrolysis and/or gasification at 400-1100 C in a fluidized bed reactor containing a bed of inert material such as refractory sand using air or mixtures of O2, N2, CO2, and water as the fluidizing gas. Another object is to provide pyrolysis apparatus including a shredder (3), a dryer (4), a gasifying chamber (20), and cyclone separator (38). Separated gases are burned in boiler (62) providing steam to dryer (4) and for electricity generation, or condensed to produce oil. Separated ash is recycled to gasifier (20) and removed to storage (54). Fluidizing gas is provided through port (26) and distributing plate (22).

Description

FLUIDIZED-BED PROCESS TO CONVERT SOLID WASTES TO CLEAN ENERGY

Background of The Invention

World population growth has led to cultivation of more land, to greater demand for energy and to increasing pollution of the environment. These trends have increased the volume of agricultural wastes and other biomass materials and the need to find non-polluting ways to tap the energy locked inside them.

One example is the disposal of rice hulls, the indigestible chaff removed from the edible rice grains during milling. Tneir food value is so low that they are not suitable for fodder. P.K. Mehta and N. Pitt estimate in 2 Resource Recovery and Conservation 23-38 (1976) that annual world production of 300 million tons of paddy rice results in 60 million tons of hulls. Plowing them under results in stunted plants and reduced yield. Open field burning of the hulls creates unacceptable air polution. Burning in conventional boilers results in coating of internal parts by molten ash, air pollution and no by-products except ash for making cement or rubber fillers.

Applicants have discovered that pyrolysis, or decomposition by heat with less than total oxidation, of biomass materials in a fluidizεd-bed reactor will produce low BTU gs, pyrolytic oil, and a carbonaceous solid ash high in silica concentration without significant air pollution. A lower operating temperature than conventional boilers prevents melting of ash and slagging, yet efficiency and heat transfer rates are greater and response time to changes in steam demand is shortened. A greater turndown range increases operating flexibility.

The process will decompose not only rice hulls but also wood waste, coal, shale, cotton gin trash, wheat straw, peat, petroleum, coke, paper, peanut shells, coffee grounds, bagasse, municipal solid waste and rubber products such as tires. Features of the Invention

In accordance with the process of the present invention, the biomass material is shredded or otherwise treated so as to reduce the particle sizes to acceptable dimensions. At the same time, the material may be dried so as to reduce its moisture content. The material is then fed to a pyrolizer or gasifier in the form of a fluidized-bed reactor vessel. The gas for fluidization may be supplied by a positive displacement blower or some similar machine, and pressure relief valves may regulate the pressure in the bed. The yield products of gas, oil and char that leave the vessel are separated by a cyclone separator or some other such device, and the gas and oil may then be used as an energy source for any number of purposes. For example, they may be used to generate steam or could be used to supply the electrical needs of the system. The char may be stored in any suitable facility and may be recycled. The volume of the char is a small fraction of the volume of the original biomass material.

These and other features of the invention will be better understood and appreciated from the following detailed description when read in connection with the accompanying drawings.

Brief Figure Description

FIG. 1 is a block diagram suggesting the various steps in the process of converting biomass materials in accordance with this invention.

FIG. 2 is a diagrammatic view of a biomass conversion system utilizing the process of FIG. 1.

Detailed Description In accordance with the present invention biomass materials are gasified in a fluid bed reactor vessel to yield clean energy products in the form of oil , gas and char. The amounts of these products produced by the process depend on operating temperature , fluidization velocity and the biomass feed material employed.

Typically, the clean energy products are the following:

(a) oil - Heavy , black oil similar to No . 6 residual oil , having a heating value in the range of 10 ,000 to 12 ,000 BTU's per pound and a consistency varying from that of paint to that of a light asphalt at ambient temperature . This product can be blended with residual oil under most conditions , or it may be fired separately into either oil or coal burning facilities.

(b) char - A fine , powdered , carbon-like material, which may be burned in a fluidized-bed burner or be blended with residual or pyrolytic oil, or used on its own, as in charcoal or carbon black applications.

(c) gas - Having a heating content between 80 to 300 BTU per standard cubic foot . The gas contains large amounts of carbon monoxide and hydrogen, but it also contains between 10 and 50% water . The gas product can be easily burned in an external combustion system such as a steam boiler or gas turbine.

The process diagram shown in FIG. 1 suggests the several steps of the process of the present invention. In accordance with FIG. 1 the biomass material to be treated is fed to a shredder so as to convert the mass to a suitable size. Next , the shredded material is dried to reduce its moisture content to the moisture limitation placed on the feed material by the gasifier .

After the material has been pretreated so as to achieve the proper particle size and moisture content , it is fed to a fluidized-bed reactor having an inert bed of material such as refractory sand , alumdun balls , glass , etc. The material is thereafter gasified to yield the clean energy products of oil , char and gas.

The gasified yield is next conveyed to a separator where the char may be removed from the oil and gas , or all three of the products may be separated from one another . In the preferred embodiment of this invention , the char is returned to the gasifier to be burned in the fluidized bed . The other products , namely oil and gas , may be fired to generate steam or electrical energy , which in turn may be used in the system. For example, the electrical energy may be used to run the shredder , dryer , or blower feeding the fluidizing gas , and the steam may be used as a source of heat for the dryer.

In FIG. 2 a typical installation for carrying out the process is shown. In that figure , a storage area 1 is suggested where the biomass material (sometimes referred to as feed) is received . This material may typically be in particle sizes in the range of 2.5 x 7.5 cm. As the feed is to be processed, it is carried by belt conveyor 2 to a shredder 3 to reduce the size of the feed particles to 6 mm or less . Typically the shredder may be of the hammermill type with a capacity of 1.5 metric tons per hour . The biomass material from the shredder is next dropped into a dryer 4, which may include a conveyor screw, to reduce its moisture content below the limitation placed on the material by the system. Normally the content must be reduced to 50% or less by weight. Heat may be provided in the dryer by passing steam through the screws, and this steam may be generated by utilizing the oil and gas products yielded by the system, as suggested above. The dried feed may be conveyed by a weiφt belt 5 and elevator 6 to the fluidized-bed feed hopper 10.

The hopper 10 is connected by an air lock valve 12 and screw feeder 14 to the inlet port 16 of gasifying chamber 18 of reactor vessel 20. The interior walls of the vessel may be lined with a- refractory material, and an inert bed of materials such as sand, alumduπ balls, glass, etc. is placed on the horizontal, perforated distributor plate 22 before start-up. Tne distributor plate 22 is below the port 16 and separates the upper, fluidizing chamber 18 from the lower, air supply chamber 24 of vessel 20.

A fluidizing gas such as air or mixtures of oxygen, nitrogen, carbon dioxide and water is fed into chamber 24 during operation through a port 26 by a positive displacement air blower 28. Tne fluidizing gas for most applications will contain oxygen concentrations in the range of 0 to 21% by volume, but may be further enriched in oxygen when production of higher BTU gas is desired. Heating values of up to 500 BTU/SCF may be attained. Fluidization velocities in the range of .25 to 10 meters/second and pressures in the range of 1-8 p.s.i. are preferred. During start-up, air is fed through another port 30 from a gas burner 32 which will bring the chamber 18 up to operating temperature of 400 C to 1,100 C in about two hours.

As the biomass feed is fed through the port 16, air forced through dozens of small holes 23 in distributor plate 22 from chamber 24 fluidizes the biomass particles and mixes them with refractory sand or other inert materials used in the bed. The feed takes on the appearance of a rapidly boiling liquid, and the surrounding air stream subjects all particle surfaces to an even heat and air supply. The particles are quickly broken down into oil, gas and char/ash, which, having a greater frictional surface area-to-weight ratio than the biomass particles, is readily blown upward through an outlet port 34 at the top chamber 18 and through a pipe 36 to a conventional cyclone separator 38. The oil/gas product ratio can be adjusted by varying the operating temperatures; for example, with a biomass feed material such as rice hulls, more oil is produced near 500 C, while the gas yield increases and oil yield declines as the temperature goes to 800 C. The gas producted has a heating value of upwards of 250 BTU/SCF. Some char, comprising about 90% carbon, is produced along with the ash and is shown recycled from the cyclone 38 via an ash screw feeder 40 back through a port 42 into chamber 18 of the reactor vessel 20. It is combusted to help maintain the reaction temperature.

Some ash is continuously removed, still hot, from the cyclone by a rotary valve 44 and fed by a screwfeeder 46 under a cooling water spray 48 to an ash bucket conveyor 50. The conveyor dumps it into a chute 52 and thence into a glass storage silo 54. The silo may be equipped with its own screwfeeder 56 for unloading and hauling away the ash. This ash is largely powered silica and has only a fraction of the volume of the original biomass material, perhaps 20%. The oil and gas from the cyclone 39 are shown piped out the top of the cyclone together by duct 59 and, although the oil may be condensed, it is simpler to leave it in the vapor phase mixed with the gas for burning. As suggested above, the gas and/or oil may be utilized to generate steam for the dryer or electrical power to run any of the apparatus in the system. This is shown in the system of FIG. 2 in the form of a conventional gas burner 58 used with a forced draft fan 60 and a boiler 62 to make steam. The boiler 62 may be a standard "D" type water tube boiler designed to generate 150 pound-per-square inch (10.35 bar) saturated steam. Flue gases are discharged to the atmosphere through- a stack 64, and no emission control equipment is required due to low dust loading of the gases. Conventional boiler auxiliary systems may be used if desired.

Claims

CLAIMS:

1. A process for converting biomass material to clean energy products comprising the steps of feeding the biomass material in a predetermined particle size and having a moisture content below a predetermined limit. fluidizing the biomass with gas containing controlled amounts of oxygen, gasifying the biomass material at a temperature in the range of 400 C to 1,100 C to yield a combination of oil, gas and char, and separating the yield products.

2. A process for converting biomass material to clean energy products as defined in claim 1 further characterized by utilizing the yield products to generate energy and using that energy as needed in the process.

3. A process for converting biomass material to clean energy products as defined in claim 1 further characterized by providing the biomass material in particle sizes in the range of 1/4 inch or less with a moisture of 50% or less by weight of the material.

5. A process for converting biomass material to clean energy products comprising the steps of providing biomass material to be converted , shredding the material to reduce its size to smaller than 1/4 inch in diameter, drying the shredded biomass material to reduce its moisture content to below 50% by weight , thereafter conveying the material to a fluidized bed and simultaneously supplying a fluidizing gas with an oxygen concentration in the range of 0 to 21% by volume, gasifying the biomass at a temperature in the range of 400 C to 1 ,100 C, and removing the yield products of gas, oil and char from overhead .

6. A process for converting biomass material to clean energy products as defined in claim 5 further characterized by separating the char from the gas and oil.

7. A process for converting biomass material to clean energy products as defined in claim 6 further characterized by utilizing the gas and/or oil to generate energy , and using the energy to supply at least some of the energy needs of the process .

8. A system for converting biomass material to clean energy comprising a reactor vessel, a perforated distributor plate in the vessel, a feeder connected to the vessel for feeding biomass material into the vessel above the plate, means including a pump connected to the vessel for feeding gas containing oxygen to the vessel beneath the plate to fluidize the biomass in the vessel, a start up burner connected to the vessel to bring the vessel up to operating temperature for conversion of biomass material to a combination of gas, oil and char, a discharge duct leading from the top of the reactor vessel for removing the yield from the top of the vessel, and a separator connected to the duct for separating the yield products.

9. A system for converting biomass material to clean energy as defined in claim 8 further characterized by means connected to the separator for returning char to the vessel above the plate.

10. A system for converting biomass material to clean energy as defined in claim 8 further characterized by means connected to the separator for generating energy from the gas and/or oil yield.

11. A process for converting biomass material to clean energy products including high heating value gas comprising the steps of providing biomass material to be converted, shredding the material to reduce its size to smaller than 1/4 inch in diameter, drying the shredded biomass material to reduce its moisture content to below 50% by weight, thereafter conveying the material to a fluidized bed and simultaneously supplying a fluidizing gas with an oxygen concentration greater than 20% by volume, gasifying the biomass at a temperature in the range of 400 C to 1,100 C and removing the yield products of gas, oil and char from overhead.

12. A process for converting tires to clean energy products comprising the steps of feeding the tire material in a predetermined particle size range and having a moisture content below a predetermined limit, fluidizing the tires with gas containing controlled amounts of oxygen, gasifying the tires at a temperature in the range of 400 C to 1,100 C to yield a combination of oil, gas and char, and separating the yield products.