INTERCHANGEABLE QUENCH GAS INJECTION RING

Abstract: An apparatus for injecting quench gas (cooled syngas) through an injection ring located around the circumference of the gasifier exit duct and having ports in communication with the interior of said duct to achieve thorough mixing of the gasifier gas with the injected quench gas. Interchangeable rings having different configurations and dimensions of the ports may be used to accommodate various types of coal. The rings may be fabricated in sections for ease of maintenance and replacement.

Description: The invention relates to a process for the gasification of coal in suspension wherein the product gas, called synthesis gas or syngas, is cooled by feeding back cleaned and cooled product gas into the product gas as it leaves the gasifier unit. In particular, the invention relates to an apparatus for injecting quench gas in a gasification reactor. Processes for the gasification of coal in suspension have been known since the l940′s. In order to avoid the fouling of heat transfer surfaces of the waste heat boilers used in a conventional process for the gasification of coal, it is necessary to solidify the liquid slag droplets that are entrained in the gas leaving the gasifier, and to cool the liquid slag droplets to a temperature at which they are not sticky. This means that the entire gas stream leaving the gasifier must be cooled to a temperature that is about 38°C below the slag softening temperature. For most coals the softening temperature of the ash is in the range of about l037°C to l3l6°C. It is customary to operate the gasifier at a temperature of about l482°C and to quench the hot gas just as it leaves the gasifier but before it enters the waste heat boiler. As shown in U.S. Patent Specification No. 3,963,457 the Koppers-Totzek process (KTP) is recognized and understood by those skilled in the art to be a process for the gasification of coal in suspension. Previous gasifiers, such as the KTP, utilized spray water from the primary water pump into the stream of product gas just as it left the gasifier in order to cool the product gas and solidify the liquid slag droplets entrained therein. The use of spray water caused a large heat loss in the product gas however and, to eliminate this large heat loss, according to said U.S. Patent Specification No. 3,963,459 the process is improved by recycling cleaned and cooled product gas back into the product gas as it leaves the gasifier unit thereby cooling the product gas and eliminating the need for water sprays. This improved the thermal efficiency by a significant amount. It is therefore an object of the present invention to improve upon the said known process by providing a special injection ring having high velocity nozzles for injecting quench gas (recycled cooled and cleaned product gas) in a uniform but intense manner into the raw product gas as it exits the gasifier unit. The injection ring forms a protective annular layer of cool gas around the hot gas jet emanating from the reactor outlet duct thereby preventing hot sticky slag particles from contacting the quench pipe wall and thus eliminating slag accumulation. The injection ring is interchangeable with other injection rings, having different configurations and dimensions thereby facilitating the use of differing particulate coal solids in the gasifier. The specific design further provides ring fabricated in sections for ease of replacement and maintenance of the injection ring. The invention therefore provides an apparatus for injecting quench gas in a gasification reactor characterized by: an injection ring formed by at least two circular sections, each of said sections having an outer circular portion and an inner circular portion spaced inwardly of and concentric with said outer portion thereby forming a circular space between said inner and said outer portions, and a plurality of bores defining passageways in said inner portion and extending radially therethrough; a base plate and a top plate matingly secured to said sections and defining with said circular space a plenum chamber, said top plate having a gaseous fluid port therein in gaseous fluid communication with said plenum chamber; and means for injecting a quench gas into said gaseous fluid port. It can be remarked that FR-A-2,274,884 discloses a system for quenching a hot gas. However, the specific interchangeable quench gas injection ring of the invention has not been disclosed. The invention will now be described by way of example in more detail by reference to the accompanying drawings, in which: Fig. l is a simplified block diagram of a portion of the coal gasification system employing the invention; Fig. 2 is an elevation, partly in section, of the reactor/ quench section of fig l; Fig. 2A is an enlarged elevation of the injection ring assembly of the invention; Fig. 3 is a drawing, partly in section, of the injection ring assembly of the invention taken along line III-III of Figure 2A; and Fig. 3A is a cross section of the injection ring assembly of the invention taken along line IV-IV of Fig. 3. Referring now to Fig. l, a simplified block diagram of the pertinent portions of the coal gasification system utilizing the instant invention is shown. Pulverized coal from the coal feed system l0 is fed into the burners ll of the reactor l2 along with oxygen l4, including oxygen-enriched air, and/or steam l6. The reactor l2 is provided with a steam outlet l2a and a boiling feed water supply l2b. Ash, in the form of slag, gravitates into a slag bath tank l8 and thereafter is conveyed to a receiving bin for disposal (not shown). Product gas, containing entrained liquid slag droplets, rises in the reactor to the quench section 20, where the liquid slag droplets are solidified, and exits the reactor via duct 22 into the waste heat boiler (WHB) or syngas cooler 24 provided with a high pressure saturated steam outlet 24a and a boiling feed water supply 24b. Solids in the form of fly ash gravitate to the dry solids removal section 26 such as a cyclone separator. The slag bath bleed 28 is fed into the wet solids removal section 30, along with the overhead gas 32 from the cyclone separator 26. A portion of cleaned and cooled gas 34 from the wet solids removal section 30 is then fed back, by means of recycle gas compressor 36, into the quench 20 of the reactor l2. The quench gas 38 entering the quench 20 cools the product gas such that entrained fly slag particles are solidified and will not stick to duct 22 or waste heat boiler surfaces 24 as the solids and gas pass through. The remainder A of the product gas is further cleaned and cooled in a cooler and separator 30b and a means for acid gas removal 30c. Water is supplied via a line 30d. The resultant slurry from the wet solids removal section 30 is directed to a water cleanup section 30a provided with a steam supply B and outlet C prior to re-use or discharge via a line D. When the quench gas leaves the section 30, it is clean and relatively cool. An alternate source of recycled gas is the gas leaving the waste heat boiler, or the gas leaving the section 26. Using recycled gas from these alternate sources, especially the waste heat boiler source, would further increase the thermal efficiency, but any solid matter in the gas could be troublesome to the operator of a plant. The function of the reactor or gasifier unit l2 is to provide an appropriate volume (residence time) and appropriate mixing conditions to gasify pulverized coal with oxygen and, if required, some steam. The three reactants - coal, oxygen and steam - are introduced into the reactor l2 through diametrically opposed burners ll. Referring to figs. 2, 2A, 3 and 3A wherein the same reference numerals indicate the same means, the reactor l2 is a cylindrical vessel with an outer pressure shell 58 and a water-cooled, refractory lined inner membrane wall 48 which is cooled by generating approximately 62 bara saturated steam. The reactor l2 is a pressurized, entrained-bed gasifier operated under slagging conditions at pressures on the order of 25 bara while the temperature is maintained high enough to melt the mineral matter in the coal. The reactor l2 is provided with a gasifier exit duct 54 which is surrounded by the quench 20. The quench 20 comprises an apparatus 50 for injecting quench gas in the gasification reactor comprising a base plate 56; a top plate 57; an injection ring 55, 55a, 55b, 55c having an inner diameter and an outer diameter fixedly secured between said base plate and said top plate; plenum means 52 located within said apparatus; means 47, 5l for supplying a gaseous fluid 38 to said plenum means 52; and a plurality of passageways 53 communicating between said plenum means 52 and said inner diameter of said injection ring. The said base plate and said top plate each have a central opening therein aligned with the inner diameter of said injection ring. Advantageously the said central openings and said inner diameter are of the same dimension. More advantageously, the said injection ring comprises two semi-circles. In another advantageous embodiment of the invention the said injection ring comprises four sections formed by radials of said injection ring. In that case said four sections may be equal. Advantageously, the said passageways 53 comprise bores having diameters in the range of 5-25 mm. More advantageously said passageway bores are equal. The molten slag runs down the membrane wall 48 to the bottom of the reactor and exits through a slag tap into the slag bath l8 (not shown in fig. 2). Raw syngas containing fly ash particles leaves the top of the reactor through duct 22 (not shown in fig. 2). The diameter of the reactor l2 must be large enough to minimize the effects of flame impingement and excessive heat flux on the membrane wall 48, while the length of the reactor l2 must be large enough to provide sufficient residence time/breakthrough time for the desired carbon conversion to take place. On the other hand, too large a diameter or length would increase heat loss to the membrane wall 48 and thereby reduce the efficiency of the process. The quench 20 is a critical item in a coal gasification process where the system is designed to operate successfully for any type and grade of coal and in which all of the quench fouling parameters are present, such as in the present system. Because so many phenomena interact, the quench problem is exceedingly complex. Fouling is influenced by aerodynamics, thermal and dynamic particle history, and adhesion of particles to the wall. The actual gasifier environment poses a critical test for new quenches. Sharp temperature transitions between the reactor outlet and the quench zone are required and fouling in the lower part of the quench must be prevented. Further, a large diameter allows more time for particles to cool prior to impaction on the walls. Fouling has been shown to relate strongly to coal conversion (reactor outlet temperature) and on coal type. In the instant coal gasification system, cleaned and cooled product gas is recycled from the gas cleanup section 26, 30 to provide a quench through the line 38 for cooling the product gas. A compressor 36 is provided to pressurize the recycle gas for a range of expected quench conditions and coal types. Another condition for recycle gas requires the use of high velocity quench nozzles to provide intensive mixing during the quench. The purpose of the quench 20 is to cool the reactor l2 exit gas (product gas) from approximately l250-l500°C down to a level such that the entrained fly slag particles will be sufficiently solidified and will not stick to the syngas cooler surfaces. High pressure saturated steam at approximately 78-l05 bara is generated in the tubes 45. The quenched gas is cooled further in a duct 22, heat from the gas being transferred by radiation and convection to boiling water circulating in tubes (not shown) lining the duct. The function of the syngas cooler or waste heat boiler 24 is to further cool the gas and to recover waste heat, as high pressure steam, skilled in the art that the invention could be used in other applications, such as under differing temperature and pressure conditions, or in any process where hot process gases must be rapidly cooled by another gas and the process is carried out in a vessel with an internal water-cooled membrane wall. The invention could even be used in non-cooled reactors with thick refractory linings.

Claims: An apparatus for injecting quench gas in a gasification reactor characterized by: an injection ring formed by at least two circular sections, each of said sections having an outer circular portion and an inner circular portion spaced inwardly of and concentric with said outer portion thereby forming a circular space between said inner and said outer portions, and a plurality of bores defining passageways in said inner portion and extending radially therethrough; a base plate and a top plate matingly secured to said sections and defining with said circular space a plenum chamber, said top plate having a gaseous fluid port therein in gaseous fluid communication with said plenum chamber; and means for injecting a quench gas into said gaseous fluid port. The apparatus as claimed in claim 1 characterized in that said at least two circular sections comprise two semi-circular sections. The apparatus as claimed in claim 1 characterized in that the injection ring comprises four equal sections.. The apparatus as claimed in claim 1 characterized in that said passageways comprise bores having diameters in the range of 5-25 mm. The apparatus as claimed in claim 4 characterized in that said passageway bores are equal.

Inventors: SEGERSTROM, CLIFFORD CHARLES
Applicants: SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ B.V.
Application year: 1989
Main classification: C10J3
IPC codes: C10J3