GB2124648A

GB2124648A - Combined dryer/gasifier

Info

Publication number: GB2124648A
Application number: GB08221593A
Authority: GB
Inventors: Amelio Cicuttini
Original assignee: Unilever Bestfoods North America
Current assignee: Unilever Bestfoods North America
Priority date: 1982-07-26
Filing date: 1982-07-26
Publication date: 1984-02-22
Also published as: EP0100188A2; GB2124648B; BR8303770A; EP0100188A3; ZA834241B

Abstract

The system comprises a drying component which will effect a drying process comprising means for providing heat to wet materials in order to evaporate at least a portion of the water contained in such materials into a gas comprising, at least in part, oxygen, and means to duct off the gas which then comprises at least oxygen and water vapor; and a gasification component comprising means to supply fossil fuel, means to supply a gas comprising at least in part oxygen and water vapor in the proportions required for gasification, means for extracting at least one fraction produced by the gasification reaction, and means for utilizing the excess heat generated by the gasification reaction; wherein at least a portion of the gas supplied to the gasification reaction is the gas generated and ducted off in the drying process.

Description

1 GB 2 124 648 A 1

SPECIFICATION Combined dryer/gasifier

Summary of the invention The present invention relates to a combined system for the drying of wet materials and the gasification of a fossil fuel. In particular, the present invention comprises a combined system which comprises a drying component which will effect a drying process comprising means for providing heat to wet materials in order to evaporate at least a portion of the water contained in such materials into a gas comprising, at least in part, oxygen, and means to duct off the gas which then comprises at least oxygen and water vapor; and a gasification component comprising means to supply fossil fuel, means to supply a gas comprising at least in part oxygen and water vapor in the proportions required for 10 gasification, means for extracting at least one fraction produced by the gasification reaction, and means for utilizing the excess heat generated by the gasification reaction; wherein at least a portion of the gas supplied to the gasification reaction is the gas generated and ducted off in the drying process.

Background of the invention

Coal-fired boilers have traditionally been used to provide heat and electric power for various 15 manufacturing processes. However, such traditional methods have, in recent years, become less satisfactory.

From an environmental standpoint, the burning of coal has resulted in substantial pollution of the air. In urban environments, the air quality has deteriorated from unsightly to unhealthy over the past few decades. Most larger industrial plants burned the cheaper grades of coal which contained the greatest proportions of impurities. Environmental concerns have led to, for example, the increased use of low- sulphur coal to limit the amount of sulphur dioxide introduced as an environmental pollutant. The higher cost of such grades of coal has increased industrial costs.

More recently, higher energy costs, have become prevalent, particularly for energy sources such as oil which are controlled, for the most part, by a small group of countries. Industries which had turned 25 away from coal use because of the environmental concerns discussed above have found the rising cost and occaisionally limited availability of oil to be a major hinderance to efficient production.

One method which has been explored as a way of utilizing coal and other less-expensive fossil fuels as an energy source while reducing the problems of pollution or the costs associated with pollution control, has been gasification.

United States Patent 2,946,670 to Whaley shows a method for the gasification of solid carbonaceous fuels. A dispersion of solid carbonaceous fuel in a gasiform carrier is mixed with uncombined oxygen and passed through an elongated reaction zone of restricted crosssectional area. The fuel and oxygen are reacted therein to produce gases such as carbon monoxide and hydrogen.

United States Patent 2,987,387 to Carkeek and duptill shows a method for the production of 35 carbon monoxide from solid fuels. This is accomplished by forming a feed mixture of solid fuel in a gasiform carrier fluid, separating a portion of that carrier fluid, reacting the solid fuel and remaining carrier fluid with oxygen and contacting the hot reactants with the separated carrier fluid effecting conversion of a portion of the carrier fluid to useful products.

United States Patent 3,847,563 to Archer and Keairus shows a multi-stage fluidized bed coal 40 gasification apparatus. The apparatus is intended to totally gasify coal to form a low sulphur, gaseous fuel. ' The apparatus employs two fluidized beds. In the first bed, coal is mixed with recirculated char and dolomite or lime to remove the sulphur. The char from the first bed is then totally gasified in a second fluidized bed.

United States Patent 3,871,839 to Moody shows a method of feeding solidcarbonaceous material to a high temperature reaction zone. The method includes forming a slurry of the carbonaceous material in a liquid vehicle, raising the internal pressure of the slurry to the operating level of the gasifier, drying the carbonaceous material by entraining such material in a hot gas stream, then separating the carbonaceous material and feeding it to the gasifier.

Gasification of coal still represents a source of pollution, however, gasifiers in general represent 50 systems which are more manageable from a confinement standpoint. This has resulted in lower costs.

In addition, experience has shown that the separation of sulphur from hydrogen sulfide has produced in the gasification of coal is less costly than separation of sulphur from the sulphur dioxide produced in the ordinary firing of coal.

Gasification requires oxygen and steam as process inputs as well as a feedstock of fossil fuel. U.S. 55 Patent 4,284,416 to Nahas suggests that at least a portion of the steam may be supplied from the moisture present in a slurried fossil fuel. This reference provides for an integrated coal dryer and steam gasification process. The reference provides that carbonaceous solids slurried in an aqueous solution, which preferably contain catalyst constituents having gasification activity, are dried by contacting the slurry with super heated steam in a fluid bed slurry dryer and the resultant dried solids are subsequently 60 gasified with steam generated in the dryer. This practice is specific to the individual system described however. The carbonaceous solids are first slurried, preferably to provide the catalyst contact. The 2 GB 2 124 648 A 2 solids are dried without the presence of oxygen, presumably to prevent premature gasification, and the drying is accomplished under pressure.

Many industrial processes require the drying of wet materials before further processing or as the final step of processing. This drying is often energy intensive and results in the production of excess heat which cannot be further utilized. In addition, such drying processes may remove impurities along with water vapor, and such impurities may result in additional pollution unless additional treatment is provided.

Objects of the present invention It is an object of the present invention to provide a combined system for the drying of wet materials and the gasification of a fossil fuel.

It is a further object of the present invention to provide a combined system in which the oxygen and water vapor requirements of a gasificiation process may be completely provided by the off gases of an industrial drying process.

It is still a further object of the present invention to provide a combined system in which any impurities passed off with oxygen and water vapor in an industrial drying process are incinerated during the gasification of a fossil fuel.

It is still another object of the present invention to provide a combined system in which the exhaust heat from an industrial drying operation may be at least partially recovered for use in the gasification of a solid fuel.

The other objects, features and advantages of the present invention will become more apparent 20 in light of the following detailed description of the preferred embodiment thereof.

According to the present invention, there is provided a combined system for the drying of wet materials and the gasificiation of a fossil fuel, which combination comprises a drying component which will effect a drying process comprising means for providing heat to wet materials in order to evaporate at least a portion of the water contained in said materials into a gas comprising, at least in part, oxygen, 25 and means to duct off the gas which then comprises at least oxygen and water vapor; and a gasification component comprising means to supply fossil fuel, means to supply a gas comprising, at least in part, oxygen and water vapor in the proportions required for gasification, means for extracting at least one fraction produced by the gasification reaction, and means for utilizing the excess heat generated by the gasification reaction; wherein at least a portion of the gas supplied to the gasification 30 reaction is the gas generated and ducted off the drying process.

Brief description of the drawings invention.

Figure 1 is a diagram which illustrates the operation of a typical industrial drying operation.

Figure 2 is a diagram which illustrates the operation of a typical gasification operation.

Figure 3 is a diagram which illustrates the operation of a combined dryer gasifier of the present 35 Detailed description of the invention

Gasification processes which are presently known operate on the principle that coal, or another similar, generally solid fossil fuel, can be converted into simple compounds. In the presence of sufficient water and oxygen, gasification of coal will produce simple compounds such as carbon monoxide, hydrogen gas, methane and others, all of which are generally gaseous at about ambient temperature.

The most significant reactions which take place in the gasification process are:

(1) (2) (3) (4) Kcal C+1-1,0+311.21--CO+1-12 Mol Kcal C+2H,--CH4+21.9Mol C0+1-120--->C02+1-12+9.8 Kcal Kcal Mol C+C02+41.2---)2C0 Moi These involve both endothermic and exothermic reactions. For gasification to proceed, therefore, either heat must be supplied, or there must be combustion of some part of the carbon, according to the 50 reaction.

3 GB 2 124 648 A 3 (5) C+02--C02+94 Kcal Mol In most gasification processes the partial combustion of carbon yields a positive balance of heat overall. This heat is generally utilized to form steam, which is normally returned to the gasifier as part of the supply feedstream. The heat, therefore, is generally utilized in both the form of reactive heat and in 5 the form of sensitive heat increasing the temperature of the gas output.

Obviously, the overall thermal efficiency of the gasifier, defined as:

Energy input from fuel, oxygen and steam (Kcal) Energy output in output steam and gases (Keal) will be dependent on the type of fuel used and the level of impurities, such as moisture, ashes, volatiles, sulphur and the like, contained therein.

The gasification systems which are known from literature and those which are in actual operation10 can be very different in structure and process requirements. These will, of course, depend on the type of coal intended to be used in any particular system. There is no limitation on the use of any type of gasifier for the practice of this invention, provided the gasification process is one which requires the input of water vapor, together with various proportions of oxygen.

Likewise, the drying systems required in various industrial processes will also vary a great deal. 15 Such systems are specifically designed to accomoclate considerations such as the materials to be dried and the method of heating, as well as various limitations which might be imposed because of environmental concerns. All such drying systems will produce water vapor as an exhaust gas. Various proportions of air or other gases may be mixed with the water vapor, as well as various impurities in the form of particulate solids, liquids or gases. A large amount of heat is generally given off as well. 20 It is fairly common in such processes, that exhaust gases must be treated to remove impurities and recover available heat. Sophisticated systems exist which employ multiple pass drying in order to provide the necessary incineration of impurities and still maximize the utilization of energy. In other systems the water vapors are condensed in specially designed heat exchangers, This will reduce air pollution, but will result in disposal problems for the condensate.

The drying system may be provided with heat by several methods, including direct contact of the heating medium with the product, indirect contact or some combination of these two applications.

One area of industrial application which requires extensive drying operations is in the starch wet milling industry. In the maize wet milling industry, for example, it is common to use contact-type dryers in which various product materials are heated by direct contact with pipes containing steam. Air is often used to remove the water vapor generated in this way. Of course, drying of solid or liquid products could be accomplished at positive pressures without any use of air or other gas to assist in the removal of vapors. However, the use of air in this manner is beneficial in limiting the temperature increase in the product materials, which might be detrimental, and in preventing condensation within the drying equipment. Various types of indirectly heated dryers can be employed, and these are variously described as rotating tube bundle type dryers, multi-stage pipe dryers, tray dryers, etc. It is also common to use dryers which employ only heated air, and these are variously described as flash dryers, rotary flash dryers, spray dryers, and by other common terms.

The composition of the exhaust from any of these dryers will depend on the volume of air or other gas which is used to carry off the vapors. Also, the particular material being dried and the drying 40 temperature will determine the amount and composition of any impurities, particularly volatile impurities.

The water vapor content will be approximately equal to the water released by the wet materials during the drying process, and the temperature will depend on the various drying conditions.

In a drying process which uses indirect heating with steam in a bundle tube dryer, for example, 45 the composition of the exhaust gases--can usually be adjusted to maintain a desired ratio of air to water vapor. A typical industrial drying operation is shown in the diagram of Figure 1. As shown in this Figure, product wet material, air and steam are introduced into a drying apparatus, and dry product, steam condensate and exhaust gases are generated. The exhaust gases will contain air and water vapor, it may also include any impurities removed from the product wet material, such as particulate solids, 50 liquids or gases. The amount of steam necessary to effect drying will depend on the temperature of the input air and wet materials, the moisture content of the product and thermal efficiency of the equipment.

The present invention combines a drying system, such as the one just described, with a gasifying system. Such a combination is most advantageous when the exhaust gases of the dryer is equivalent to 55 the requirements of the gasification process.

Such a gasification process is depicted in Figure 2. In the diagram shown in that Figure, coal, or another fossil fuel is provided to a gasifier apparatus and converted to simple gaseous compounds, such as carbon monoxide, hydrogen gas, methane and others, which are given off.

4 GB 2 124 648 A 4 The gasifier shown in Figure 2 also requires the input of water vapor and oxygen. The oxygen required may be provided in the form of air or another gas containing oxygen. The gasification reaction involves both endothermic and exothermic reactions described more completely above. The balance of energy is usually positive and part of this energy is given off in the form of steam which is, in the normal practice, recycled to the gasifier, as illustrated by the recycled stream system depicted in Figure 5 2.

In Figure 3, a combined dryer-gasifier is depicted. In the illustrated embodiment, the dryer component operates in the same manner as the dryer illustrated in Figure 1. In the embodiment of Figure 3, however, the gas generated and ducted off the dryer component, which gas contains at least oxygen and water vapor, is fed directly into the gasification component to meet the requirements of the 10 gasification process. Also, in the embodiment illustrated, the excess heat generated in the form of steam as a result of the gasification process, rather than being recycled in the manner illustrated in Figure 2, is employed as input steam to the drying operation. Since this steam isutilized to generate the water vapor employed in gasification, it is believed that this energy is effectively conserved.

Various alternatives to the illustrated embodiment are available which also utilize the present 15 invention.

The output gases of the gasifier component are assumed to be intended to provide energy for the industrial process, in place of the traditional coal-fired boiler. The gases, therefore, can be used to fire a boiler for the production of process steam, for steam which can be used to power a turbine to produce plant electricity, or for any other use desired. In this regard, it should be noted that the gas produced by 20 the gasifier can be produced in fractions. The fractions can be provided in one or more streams depending on the intended subsequent use.

If a gas turbine is to be powered, then it is convenient to use a two pass gasifier apparatus of the kind well known to the art. Such a gasifier would be capable of directly producing a clear gas fraction which would require very limited purification. At the same time, the gasifier would produce a top gas 25 rich in tars and oils which would be useful in firing a furnance, or the like. Thus, each gas fraction may be employed for a separate use.

Example

A combined dryer gasifier could be employed in the corn wet milling industry in the following manner. Assuming a hypothetical grind of one thousand (1000) tons per day of corn having a fifteen 30 percent (15%) moisture content, the corn wet milling process would be expected to yield approximately the following products:

Fibers 93.5 tons per day, dry basis (11 % dry basis) Steepwater 5 1.0 tons per day, dry basis (6% dry basis) Gluten 59.5 tons per day, dry basis (7% dry basis) Germ 51.0 tons per day, dry basis (6% dry basis) The drying requirements of these products would be expected to be:

Fibers - Predrying from about 58% moisture to about 2 5% moisture - Second Drying from about 25% moisture to about 12% moisture Steepwater- Drying from about 50% moisture to about 12% moisture Gluten - Drying from about 58% moisture to about 12% moisture Germ - Drying from about 49% moisture to about 5% moisture The actual amounts of water which must be removed from these product materials would be:.

Fiber predrying Water content Ca, 58% moisture - Water content@ 25% moisture = Waterremoved 45 93.5tons 93.5 tons 224 tons/day - 124 tons/day or 0. 1 tons of water per ton of commercial grind (15% moisture).

tons/day Fiber second drying Water content Ca 2 5% moisture - Water content Ca, 12% moisture = Water removed 50 93.5tons 93.5 tons 124 tons/day - 106 tons/day 18 tons/day or 0.018 ton of water per ton of commercial grind (15% moisture).

Steepwater drying Water content (a- 50% moisture - Water content Ca 12% moisture = Water removed 55 51 tons 51 tons 102 tons/day - 58 tons/day or 0.044 ton of water per ton of commercial grind (15% moisture).

44 tons/day GB 2 124 648 A 5 Total removal requirements for Fiber second drying and Steepwater=62 tons/day or 0.062 tons of water per ton of commercial grind (115% moisture).

Gluten drying Water content C 58% moisture - Water content (a, 12% moisture Water removed 141.66 tons/day - 67.61 tons/day = 74.05 tons/day 5 or 0.074 tons of water per ton of commercial grind (15% moisture).

Germ drying Water content Ca 49% moisture - Water content Cw 5% moisture = Water removal tons/day - 53.68 tons/day = 46.32 tons/day or 0.04632 tons of water per ton of commercial grind (15% moisture).

Total drying requirements for 1000 tons=282.37 tons/day or 0.282 tons of water per ton of commercial grind (15% moisture).

As an example, a two-stage gasifier has been developed by IGI S.p.A. in Italy. This gasifier is said to provide a final gas mixture (top and clear or bottom gas, excluding tars and oils) having the following 15 composition:

CO, CnH.. CO H, CH4 N2 4.4% volume 0.4% volume 27.2% volume 15.4% volume 3.0% volume 49.6% volume IGI has given the following values for the gasifier's thermal efficiencies:

90% for non-dertarred output gas 82% for cletarred output gas 78% for cold, cleaned output gas The caloric value of the output gas is given as 1543 kilocalories per normal cubic meter (Kcal/N M3). This data is for gasification of sub-bituminous coal with a low caloric value (LCV) of 6700 kilocalories per kilogram (Kcal/kg), using air and steam. Output gases with higher caloric values would be obtained in oxygen enriched gas were to be used instead of air.

The amount of steam produced and air used in a gasifier of 4 tons per hour (t/h) coal capacity is 30 as indicated in the following balance for cold pure gas equivalent and starting from a type of coal having 6,700 Kcal/kg of LHV:

Kcal(LI-IV) 106 Kcal(LI-IV) (Coal input 96 tons per day (t/d) x63x 106 =643 x ton day - Steam produced and injected 27.8 t/d (17.7 x 1 O'Kcal/day) or 0.29 tons per ton of coal Air input 193,000 Nm/day or 2010 Nm/ton of coal Kcal(LI-IV) - Gas output 310,000 Nrnl/day (1543 or 476x 1 01Kcal/day Nm3 -Tar and oil---8% of coal heat input or 51.5x l OcKcal/day Utilizing these results, gasification of one ton of coal requires approximately:

Air 2,040 NmI Steam 0.29 tons 40 Employing the above gasifier at a rate of four tons of coal per hour (4 t/h) would require:

Air - 2,040x4=8,160 Nml/hr.

Steam - 0.29 x4=1.1 6 ton/hr.

Consequently, the requirements for the operation of one gasifier at a rate of four tons of coal per hour can be completely supplied by, for example, the water vapor produced by the fiber predrying 45 operation at daily grind rate of 280 tons per day.

6 GB 2 124 648 A 6 Fiber pre-drying tons water vapor 1.16 hour 0.1 1.16 tons water vapor ton of grind tons water vapor hour 0.018 tons of water vapor day ton of grind hours tons of grind x24-2-'280 day Fiber second drying day hours tons of grind x24----1 550 day Steepwater drying 5 tons water vapor 1.16 hour hours tons of grind x24 ---630 0.044 tons of water vapor day ton of grind day Combined fiber second drying and steepwater drying tons water vapor 1.16 hour 0.062 tons water vapor ton of grind 1.16 tons of water vapor hour hours tons of grind x 2 4 ----4 5 0 day Gluten day hours tons of grind x 2 4 -f-:--3 7 5 10 0.074 tons water vapor day day ton of grind 1.16 tons of water hour 0.04632 tons water vapor day ton of grind Germ hours tons of grind x24-2--600 day The preferred use of the present invention would be in utilizing the water vapor released in the second drying of the Fiber and the Steepwater. These are the drying areas which have the greatest problem with the emission of impurities, and therefore require the greatest amount of anti-pollution 15 treatment.

Other features, advantages and specific embodiments of this invention will become readily apparent to those excercising ordinary skill in the art after reading the foregoing disclosures. These specific embodiments are within the scope of the claimed subject matter unless expressly indicated to the contrary. Moreover, while a specific embodiment of this invention has been described in considerable detail, variations and modifications of this embodiment can be effected without departing from the spirit and scope of the invention as disclosed and claimed.

4 9 7 GB 2 124 648 A 7

Claims

1. A combined system for the drying of wet materials and the gasification of a fossil fuel, which combination comprises:

a) a drying component which will effect a drying process comprising i) means for providing heat to wet materials in order to evaporate at least a portion of the water 5 contained in said materials into a gas comprising at least in part, oxygen, and ii) means to duct off the gas which then comprises at least oxygen and water vapor; and b) a gasification component comprising i) means to supply fossil fuel, ii) means to supply a gas comprising at least in part, oxygen and water vapor, in proportions 10 required for gasification, iii) means for extracting at least one fraction produced by the gasification reaction, and iv) means for utilizing the excess heat generated by the gasification reaction.

wherein at least a portion of the gas supplied to the gasification reaction in (b)(ii) is the gas generated and ducted off in (a)(ii) of the drying process.

2. The system of claim 1 in which all of the gas supplied to the gasification reaction in (b)(ii) is the gas generated and ducted off in (a)(ii).

3. The system of claim 1 or 2 in which the gas generated and ducted off in (a)(ii) contains impurities which are incinerated in the gasification process.

4. The system of claim 1 in which exhaust heat from the drying process is transferred from the 20 drying component by the gas generated and ducted off in (a)(ii), and is at least partially recovered in the gasification component.

Printed for Her Majesty's Stationery Office by the Courier Press, Leamington Spa, 1984. Published by the Patent Office, Southampton Buildings, London, WC2A 1 AY, from which copies may be obtained.