Behind the brick thermocouple

The invention is a thermocouple installation wherein the thermocouple measures the temperature in a gasification reactor. The thermocouple is installed through the wall of a gasification reactor such that the measuring element is behind a continuous layer of refractory hot face brick. The thermocouple assembly is mounted in a opening made through the gasifier wall, the insulating brick, and optionally a portion of the way through the hotface brick.

FIELD OF THE INVENTION
 This invention relates generally to the protection of a thermocouple used
 in a gasification process and, more particularly, to the use of refractory
 brick to extend the useful life of thermocouples used in a gasification
 process.
 BACKGROUND OF THE INVENTION
 In high temperature gasification processes, a hot partial oxidation gas is
 produced from hydrocarbonaceous fuels, for example coal, oils, hydrocarbon
 wastes, and the like. In these processes, the hydrocarbonaceous fuels are
 reacted with a reactive oxygen-containing gas, such as air or oxygen, in a
 gasification reactor to obtain the hot partial oxidation gas.
 The term "hydrocarbonaceous" as used herein to describe various suitable
 feedstocks is intended to include gaseous, liquid, and solid hydrocarbons,
 carbonaceous materials, and mixtures thereof. In fact, substantially any
 combustible carbon-containing organic material, or slurries thereof, may
 be included within the definition of the term "hydrocarbonaceous". Solid,
 gaseous, and liquid feeds may be mixed and used simultaneously; and these
 may include paraffinic, olefinic, acetylenic, naphthenic, and aromatic
 compounds in any proportion. Also included within the definition of the
 term "hydrocarbonaceous" are oxygenated hydrocarbonaceous organic
 materials including carbohydrates, cellulosic materials, aldehydes,
 organic acids, alcohols, ketones, oxygenated fuel oil, waste liquids and
 by-products from chemical processes containing oxygenated
 hydrocarbonaceous organic materials, and mixtures thereof.
 The term "liquid hydrocarbon," as used herein to describe suitable liquid
 feedstocks, is intended to include various materials, such as liquefied
 petroleum gas, petroleum distillates and residue, gasoline, naphtha,
 kerosene, crude petroleum, asphalt, gas oil, residual oil, tar-sand oil
 and shale oil, coal derived oil, aromatic hydrocarbons (such as benzene,
 toluene, xylene fractions), coal tar, cycle gas oil from
 fluid-catalytic-cracking operations, furfural extract of coker gas oil,
 and mixtures thereof.
 "Gaseous hydrocarbons," as used herein to describe suitable gaseous
 feedstocks, include methane, ethane, propane, butane, pentane, natural
 gas, coke-oven gas, refinery gas, acetylene tail gas, ethylene off-gas,
 and mixtures thereof.
 "Solid hydrocarbon fuels," as used herein to describe suitable solid
 feedstocks, include, coal in the form of anthracite, bituminous,
 subbituminous; lignite; coke; residue derived from coal liquefaction;
 peat; oil shale; tar sands; petroleum coke; pitch; particulate carbon
 (soot or ash); solid carbon-containing waste materials, such as sewage;
 and mixtures thereof. Certain types of hydrocarbonaceous fuels, in
 particular coal and petroleum coke, generate high levels of ash and molten
 slag.
 In the reaction zone of a gasification reactor, the hydrocarbonaceous fuel
 is contacted with a free-oxygen containing gas, optionally in the presence
 of a temperature moderator. In the reaction zone, the contents will
 commonly reach temperatures in the range of about 1,700.degree. F.
 (930.degree. C.) to about 3,000.degree. F. (1650.degree. C.), and more
 typically in the range of about 2,000.degree. F. (1100.degree. C.) to
 about 2,800.degree. F. (1540.degree. C.). Pressure will typically be in
 the range of about 1 atmosphere (100 Kpa) to about 250 atmospheres (25,000
 KPa), and more typically in the range of about 15 atmospheres (1500 Kpa)
 to about 150 atmospheres (1500 KPa).
 In a typical gasification process, the hot partial oxidation gas will
 substantially comprise H2, CO, and at least one gas from the group H.sub.2
 O, CO.sub.2, H.sub.2 S, COS, NH.sub.3, N.sub.2, and Ar. Particulate
 carbon, ash, and/or molten slag typically containing species such as
 SiO.sub.2, Al.sub.2 O.sub.3, and the oxides and oxysulfides of metals such
 as Fe and Ca are commonly produced by well known partial oxidation
 processes in the reaction zone of a free-flow, down-flowing vertical
 refractory lined steel pressure vessel. An example of such a process and
 pressure vessel are shown and described in U.S. Pat. No. 2,818,326, which
 is hereby incorporated by reference.
 Thermocouples are commonly used for measuring temperature in these high
 temperature processes, including the temperature in the gasification
 reactor. Thermocouples are pairs of wires of dissimilar metals which are
 connected at both ends. The content of the wires must be sufficiently
 dissimilar to allow for a difference in electrical potential between them.
 Except for the junction at the end of the thermocouple, the two wires are
 electrically insulated from each other in a protective sheath. The
 electrical insulation is commonly provided by the protective sheath which
 consists of a temperature resistant electrically insulating material
 having two non-intersecting holes extending axially through a portion of
 the length of the sheath, wherein the thermocouple wires are run through
 the holes and wherein the holes intersect one another only at one point.
 Typical protective sheath materials include high temperature, high purity
 ceramics, such as alumina. The holes may be formed by casting the
 refractory material around the thermocouple wires and sensor.
 The basis of operation of a thermocouple is that an electrical potential
 that exists between connecting metals varies with temperature. The
 electrical potential is compared to the potential of a real or an
 artificial standard that represents the same metals at a standard
 temperature, and the difference in temperature is measured by a voltage
 measuring instrument placed in the thermocouple circuit or alternatively
 by a voltage; measuring instrument that is sent signals by a transmitter
 placed in the thermocouple circuit. The choice of dissimilar metals used
 for the thermocouple will vary depending on, among other things, the
 expected temperature range to be measured. For instance, one type of
 thermocouple commonly employed under the conditions present in a
 gasification reactor has one wire that contains platinum and about 30%
 rhodium and a second wire that contains platinum and about 6% rhodium. For
 a gasification reactor, type B, type R, and type S platinum/rhodium
 thermocouples are useful.
 The thermocouples have very short lifespans in the environment present in a
 gasification process, particularly in the environment present in the
 gasification reactor. The relatively short lifespan is due in part to the
 corrosive atmosphere that prevails during the operation of the
 gasification reactor. An unprotected thermocouple left in this environment
 is quickly attacked and rendered useless. Such attack can be most severe
 when the thermocouple comes into contact with molten slag present in the
 reactor. Such a thermocouple may be rendered inoperable in minutes.
 To alleviate this problem, thermocouples are commonly inserted into a
 refractory thermowells mounted along the outer wall of a gasification
 reactor. The refractory thermowells would include barriers of
 chromia-magnesia, chromia, or similar slag resistant materials, and may
 incorporate other refractory and non-refractory materials such as Al.sub.2
 O.sub.3, MgO, sapphire, molybdenum, and stainless steel. These refractory
 thermowells do not make a complete barrier to the atmosphere inside the
 gasifier. The refractory thermowell does not stand up to pressure, and
 does not stand up to stress. It is simply a semipermeable mass transfer
 barrier that protects the thermowell from slag, direct flame, and some hot
 gases.
 When used in a gasification reactor, the thermowell may be introduced by
 passing it through an opening in the outer wall of the reactor pressure
 vessel. The thermowell may then pass through a corresponding opening in a
 refractory material, or series of refractory materials, commonly used to
 line the inner surface of the reactor pressure vessel. The thermowell may
 extend into the open space of the reactor or more typically it may be set
 back at a slight distance from the interior of the reactor.
 Unfortunately, positioning the thermocouple inside a thermowell has not
 provided a complete solution. Over time, molten slag will breach the
 thermowell. The breach is commonly due to the effects of erosion and
 corrosion as well as thermal and/or mechanical stress. The breach,
 typically small initially, allows molten slag to enter the thermowell
 where it can come in contact with the thermocouple, rendering it useless.
 It would therefore be beneficial to have a means to increase the lifespan
 of thermocouples used in a gasification process.
 SUMMARY OF THE INVENTION
 The invention is a thermocouple installation wherein the thermocouple
 measures the temperature in a gasification reactor. The thermocouple is
 installed through the wall of a gasification reactor such that the
 measuring element is behind a continuous layer of refractory hot face
 brick. The thermocouple assembly is mounted in a opening made through the
 gasifier wall, the insulating brick, and optionally a portion of the way
 through the hotface brick.

DETAILED DESCRIPTION OF THE INVENTION
 As used herein, the term "thermocouple" is a temperature sensing device
 that includes the thermocouple sensor and wires and any support,
 insulation, protection, or mounting means used incident with the
 thermocouple sensors and wires.
 As used herein, the term "hotface brick" is the layer or layers of
 refractory material or materials adjacent to the interior of the gasifier.
 As used herein, the term "thermocouple sensor" describes the point, usually
 on the distal end of the thermocouple, wherein the dissimilar metals are
 joined and where the electrical potential is generated.
 As used herein, a "thermowell" is a protective sheath that provides
 substantial barrier to gas flow and is capable of withstanding and sealing
 against pressure.
 As used herein, the terms "sheath" and "protective sheath" are used
 interchangeably to describe a body that provides support, protection, and
 electrical insulation for at least one of the thermocouple wires.
 As used herein, the term "molten slag" includes slag, ash, metals, silica,
 and other contaminants that can be fluid at reactor conditions.
 In high temperature gasification processes, a hot partial oxidation gas is
 produced from hydrocarbonaceous fuels, for example coal, oils, hydrocarbon
 wastes, and the like. In these processes, the hydrocarbonaceous fuels are
 reacted with a reactive oxygen-containing gas, such as air or oxygen, in a
 gasification reactor to obtain the hot partial oxidation gas. Gasification
 reactors are therefore specially designed partial burners. In the reaction
 zone of a gasification reactor, the hydrocarbonaceous fuel is contacted
 with a free-oxygen containing gas, optionally in the presence of a
 temperature moderator. In the reaction zone, the contents will commonly
 reach temperatures in the range of about 1,700.degree. F. (930.degree. C.)
 to about 3,000.degree. F. (1650.degree. C.), and more typically in the
 range of about 2,000.degree. F. (1100.degree. C.) to about 2,800.degree.
 F. (1540.degree. C.). Pressure will typically be in the range of about 1
 atmosphere (100 Kpa) to about 250 atmospheres (25,000 KPa), and more
 typically in the range of about 15 atmospheres (1500 Kpa) to about 150
 atmospheres (1500 KPa).
 In many applications the fuel contains significant quantities of ash. At
 gasification temperatures the ash may be partially or fully molten. It is
 generally preferred to keep the ash in the molten state until it leaves
 the gasification reactor. Otherwise, particulate matter can accumulate and
 plug the reactor. However, this molten ash, or slag, is very harsh to
 surfaces it contacts. The molten ash attacks refractory brick, and this
 brick needs to be periodically replaced.
 A gasifier must be designed to withstand the pressure within the gasifier.
 This generally required a metallic shell 10 in FIG. 1. The shell may be
 steel, molybdenum, or any suitable material. This shell must be capable of
 withstanding pressures generated in the gasifier at the highest
 temperature that the shell reaches during operation. At temperatures of
 about 2000.degree. F. (1100.degree. C.) typical of the interior of a
 gasifier the strength of steel is severely compromised.
 Therefore, there is a layer or layers of insulating brick 22 between the
 gasification zone and the shell. This insulating brick may be from about 6
 inches (15 cm) thick to well over 10 inches (25 cm) thick. The brick is
 usually present in multiple overlapping layers. The brick is made of any
 suitable refractory material. It is often alumina, chromia, magnesia, or
 mixtures thereof. The insulating brick is often cast as lower density
 material than is the hotface brick.
 The thermocouple mount must extend through an opening 32 in the gasifier
 shell and though the insulating brick. The thermal coefficient of
 expansion is different between the metallic shell and the insulating
 brick. Therefore, an the reactor heats and cools, the shell and the
 insulating brick usually move relative to one another. The opening 32
 through the shell and the insulating brick, through which the thermocouple
 extends, must be of sufficient diameter to allow the movement of the
 shell, insulating brick, and optionally the hotface brick relative to each
 other without shearing the thermocouple. In one embodiment of this
 invention the opening is between about 0.5 inches (1.3 cm) and about 6
 inches (15 cm) in diameter. The opening diameter is preferably between
 about 1 inch (2.5 cm) and about 4 inches (10 cm) in diameter, more
 preferably between about 1.5 inches (3.8 cm) and about 2.5 inches (6.4 cm)
 in diameter.
 On the inner face of the insulating brick is one or more layers of hotface
 brick 24. This hotface brick is often similar in composition to the
 insulating brick, though it is generally higher density than the
 insulating brick. This hotface brick is more thermally conductive than is
 the insulating brick. This hotface brick is made of any suitable
 refractory material, i.e., alumina, chromia, magnesia, or mixtures
 thereof. This hotface brick is exposed to the gasification zone. For
 feedstock that has significant quantities of slag, i.e., greater than
 about 0.1 percent by weight of total feed, then hotface bricks are
 preferably constructed of more slag-resistant refractory material such as
 high chromia, magnesia, or mixtures thereof.
 The hotface brick layer or layers 24 may range from about 4 inches (10 cm)
 to about 14 inches (36 cm) thickness. The preferred hotface brick
 thickness is between about 6 inches (15 cm) to about 12 inches (31 cm),
 more preferably from about 8 inches (20 cm) to about 10 inches (25 cm).
 The thermocouples have very short lifespans in the environment present in a
 gasification process, particularly in the environment present in the
 gasification reactor. The relatively short lifespan is due in part to the
 corrosive atmosphere that prevails during the operation of the
 gasification reactor. An unprotected thermocouple left in this environment
 is quickly attacked and rendered useless. Such attack can be most severe
 when the thermocouple comes into contact with molten slag present in the
 reactor. Such a thermocouple may be rendered inoperable in minutes.
 The thermocouple sensor 30 in the present invention is mounted behind a
 layer of hotface brick 24. The thermocouple 26, with or without a
 thermowell, is passed in succession straight through a opening in the
 steel gasifier shell 10 and then through an aligned opening 32 in the
 refractory insulating brick 22 and then, optionally, part way through the
 hotface brick 24.
 The temperature response, that is, the time for a change in gasifier
 temperature to be reflected in the thermocouple response, depends in part
 on the thickness of the hotface brick layer between the thermocouple and
 the gasification zone. In addition, the minor insulating effect of the
 hotface brick will result in the thermocouple mounted behind the hotface
 brick to read low. The time delay and temperature differential are more
 pronounced with thicker layers of hotface brick between the thermocouple
 sensor 30 and the gasifier interior. The thickness of the layer of hotface
 brick between the thermocouple sensor and the gasifier interior therefore
 should be less than about 12 inches (31 cm), preferably less than 9 inches
 (23 cm), more preferably less than about 6 inches (15 cm), and most
 preferably less than about 4.5 inches (12 cm). At the same time, the
 hotface brick is attacked by the molten slag and the atmosphere inside the
 gasifier, and the hotface brick may fail. Failure may be accelerated by
 stresses caused by the reduced thickness of the hotface brick in front of
 the thermocouple. Therefore, the thickness of the hot face brick is
 preferably greater than about 2 inches (5 cm), more preferably greater
 than about 3.5 inches (8.9 cm). For hydrocarbonaceous feedstock that
 produces higher quantities of molten slag, i.e., greater than about 0.1
 percent by weight slag, the thickness of the hot face brick is preferably
 greater than about 3.5 inch (8.9 cm), more preferably greater than about 4
 inches (10 cm).
 These dimensions may differ for various feedstocks. The thickness of
 hotface brick between opening containing the thermocouple and the gasifier
 interior may range from about 20% to about 100% of the thickness of the
 hotface brick, preferably from about 30% to about 66%, and most preferably
 from about 40% to about 60% of the thickness of the hotface brick to the
 extent the thickness between the opening and the gasifier interior is less
 than 100%, it is preferred that the opening extend contiguously from the
 opening in the insulating brick. The hotface brick viewed from the
 gasifier interior beneficially will not have substantial quantity of
 material removed.
 A particularly preferred embodiment of the invention has an average hotface
 thickness of about 8 inches (20 cm) to about 10 inches (25 cm) in
 thickness, a hotface thickness in front of the thermocouple of between
 about 3.5 inches (8.9 cm) and about 4.5 inches (11.4 cm), and an opening
 or opening extending part way through the hotface brick. This opening
 would be continuous with the opening extending through the shell and the
 insulating brick. The opening can be cast into the insulating brick and
 the hotface brick or can be machined into the installed brick. The opening
 should be sized, and the refractory material mounted, so that the
 thermocouple will not be sheared due to thermal expansion and movement
 during heat-up or cool-down of the reactor.
 For a four inch thickness of hotface brick in front of the thermocouple,
 with insulating brick, outer shell, and flange assembly as shown in FIG.
 1, there is a 20 to 30 second delay in the response of the thermocouple to
 temperature changes within the reactor. The thermocouple will also read
 between about 100.degree. F. (55.degree. C.) and about 300.degree. F.
 (170.degree. C.) lower than would conventionally mounted thermocouples.
 However, once known and calibrated, both factors can be accounted for in
 the operation and control of the reactor.
 The thermocouple should be mounted so as to not let the thermocouple sensor
 30 touch the refractory 22 and 24. It is preferred that the thermocouple
 sensor be located between about 0.25 inches (0.6 cm) and about 3 inches (8
 cm), more preferably between about 0.5 inches (1.2 cm) and about 1 inch
 (2.5 cm), from the rear surface of the hotface brick between the
 thermocouple sensor and the gasifier interior.
 The thermocouple 26 is comprised of a pair of wires 18. The wires have
 dissimilar metal content such that a difference in electrical potential
 can develop between them when the thermocouple is exposed to a heat
 source. The wires, for example, may both contain platinum and rhodium as
 their primary substituents with the amounts of platinum and rhodium being
 different in the two wires. For example, one of the wires may have about
 30% rhodium while the other wire has about 6% rhodium. Alternatively, one
 wire may be pure platinum and the other wire may contain 10% or 13%
 rhodium. For both wires, the remainder is primarily platinum.
 It is generally preferred to mount the thermocouple sensor at the end of a
 protective sheath 28. The wires are joined to each other at a hot junction
 30 and cold junction (not shown). The terms "hot" and "cold" are used
 because when employed to measure the temperature of a gasification reactor
 the hot junction 30 is positioned closer to the heat source. The
 difference between the electrical potential of the two wires is measured.
 It is not critical how the difference in potential is measured. In fact,
 various means are known to those of ordinary skill in the art for
 measuring the difference in electrical potential. Any of these methods can
 be used in the present invention. For example, a voltage meter can be
 placed in the thermocouple circuit. Alternatively, and preferably, the
 cold junction is provided at a temperature transmitter (not shown). The
 signal generated by the temperature transmitter can then be relayed to a
 control room or other location by signal transfer means (not shown).
 Except for the hot and cold junctions, the two thermocouple wires are
 otherwise electrically insulated from each other. While it is not critical
 how insulated, in this embodiment, the electrical insulation is provided
 by a high temperature, high purity ceramic insert or cast separate holes
 within the protective sheath 28.
 There are two embodiments of this invention. The first utilizes a
 thermowell to provide additional protection to the thermocouple. The
 thermocouple is enclosed in a thermowell extending from the flange. Said
 thermowell would create a pressure (gas) barrier allowing under some
 circumstances for the thermocouple to be serviced with the gasifier
 operating. The gas barrier may not be absolute. For instance, the
 palladium/silver thermowell described in U.S. Pat. No. 5,005,986,
 incorporated by reference herein, is permeable to hydrogen. The thermowell
 nevertheless under some conditions allows the thermocouple to be at
 essentially atmospheric pressure. However, a drawback is that the
 thermowell extends into the reactor, and a breach in the hotface brick
 will allow corrosive erosive molten slag to directly attack the pressure
 barrier. Therefore, this is not a preferred embodiment of the invention.
 The thermocouple and thermowell assembly are held in place by screwing,
 bolting or clamping the thermowell to the thermocouple flange 14. The use
 of two separate connections provides for increased efficiency in that a
 thermocouple 26 can be replaced without removing the thermowell.
 Alternatively, protective sheaths 28 can be used to protect the
 thermocouple without forming a pressure seal. At some point the
 thermocouple wires must exit the pressurized vessel. The wires pass
 through a pressure sealing fitting which contacts a bushing which fits
 into a removable flange 14. The flange 14 mates with a reducer flange 12
 that is mated to the outer steel wall 10 of the pressure vessel
 gasification reactor.
 It is preferred that the pressure seal about the thermocouple wires be made
 at a location where the temperature is considerably reduced from the
 gasifier temperature, i.e., less to 1000.degree. F. (540.degree. C.) or
 less, preferably less than 600.degree. F. (320.degree. C.), more
 preferably less than about 400.degree. F. (200.degree. C.). The pressure
 seal will therefore not be subject to attack by molten slag in the event
 of a breach in the hotface brick. Slag will solidify and not reach the
 pressure seal. In addition, elastomers or other pressure sealing
 connectors generally have a longer lifespan if not exposed to temperatures
 that exist in a gasifier. The pressure seal is generally made near or
 within the thermocouple flange 14.
 The protective sheath is generally made of any suitable refractory
 material, i.e., alumina, chromia, magnesia, or mixtures thereof. The
 protective sheath will not be exposed to molten slag, however, and can
 therefore be made with the less expensive alumina even though the reactor
 may contain molten slag. The protective sheath generally contains an
 insulator running between the two electrical connectors. In a preferred
 embodiment, the protective sheath has holes through the length of the
 protective sheath wherein the thermocouple wires are run through the holes
 and wherein the holes do not intersect one another except at one point
 where the wires join.
 In addition to the protective sheath, any other protective sheath commonly
 used or subsequently developed by one of ordinary skill in the art can be
 employed. An, additional protective sheath surrounding the thermocouple
 sensor and protective sheath, may be preferred. Such sheaths may include
 barriers of refractory and/or non-refractory materials such as Al.sub.2
 O.sub.3, MgO, chrome-magnesia, high chrome, molybdenum, stainless steel,
 or mixtures or combinations thereof. By combinations it is meant two or
 more dissimilar materials in the same sheath.
 In an embodiment of this invention, a protective sheath may be comprised of
 an inner protection sheath and an outer protection sheath. The inner
 protection sheath can be formed from a high density low porosity
 refractory, such as alumina or magnesia. A castable refractory material,
 typically a high density low porosity refractory, is then poured around
 the inner protection sheath and allowed to set so as to form the outer
 protection sheath around all but the opening of the inner protection
 sheath. Preferably, this castable high density low porosity refractory
 material is comprised of chromium oxide or chromia-magnesia.
 The hotface brick does not form a pressure seal. Therefore, there must be a
 flange or flanges 12 and 14, or other suitable assembly for sealing off
 pressure. It would be beneficial for this assembly to be removable so that
 the thermocouple can be serviced as needed. At least one flange is the
 preferred means of making the gasifier gas-tight by sealing the opening in
 the gasifier shell, and at the same time providing a means to remove the
 thermocouple for service. Instead of mating flanges, threaded caps and
 nozzles or other connection means can be used.
 The flange is beneficially protected from radiant heat emanating from the
 hotface brick and the insulating brick. Otherwise the flange may be
 excessively hot. One protective method is to have a flange attached
 outwardly from the gasifier shell and an opposing flange, with the
 thermocouple extending through the flange, and at least one, and
 preferably a plurality, of washer devices 20 within the flange body
 circling the protective sheath. These washer devices, which may have the
 appearance of donuts, circle the protective sheath. It is preferred that
 these washers or donuts be made of a pliable insulating material. Donuts
 made of kaowool are particularly preferred. Thin pliable barriers 32
 located between these donuts or washers are also beneficial.
 These donuts, washers, and thin pliable barriers seal the opening from
 radiant heat. emanating from the hotface brick. This hotface brick acts
 like a black body and can radiate heat along the path that the protective
 sheath runs in. Protective sheaths are generally straight. By blocking
 this radiant heat, the point where the protective sheath exits a pressure
 seal, and is tied in to more conventional wire, may be kept below about
 1000.degree. F. (540.degree. C.), preferably below about 400.degree. F.
 (200.degree. C.). These donuts, washers, and thin pliable barriers also
 form a partial barrier to convective heat flow.
 The use of a reducing flange 12 allows the thermocouple to be removed and
 serviced with minimum disturbance of these donuts, washers, and thin
 pliable barriers. The thermocouple itself, in this embodiment, is mounted
 on the thermocouple flange 14. External to this thermocouple flange the
 temperature may be sufficiently reduced so that the thermocouple leads may
 be joined to conventional high temperature wire, for example by a terminal
 block 16 inside conduit. This conduit may have a gas seal to prevent gas
 from migrating unimpeded to, for example, a control room. The pressure
 seal between the pressurized gasification reactor and the atmospheric
 conduit is preferably made in or adjacent to the thermocouple flange 14.
 Locating the thermocouple behind hotface brick in accordance with the
 various embodiments of the invention, amongst other advantages, increases
 the useful life of the thermocouple over conventional thermocouples
 encased in slag resistant protective sheaths.
 In another embodiments, more than one thermocouples are inserted into a
 cavity 32 behind the hotface brick, having at least a corresponding number
 of inner protection sheaths. In such an embodiment, the distal ends 30 of
 the one or more thermocouples are advantageously positioned at different
 points along the length of the protective sheath, or the protective
 sheaths extend into the cavity to different depths. It is preferred that
 the depths where the thermocouple sensor is differ by 2 inches (5 cm) or
 more from the face of the hotface brick. For example, in an embodiment in
 which two thermocouples are used, slag ultimately penetrating the
 protective sheath will generally reach the thermocouple positioned closest
 to the tip first. This thermocouple will subsequently fail. It then takes
 an additional amount of time for the slag to reach and cause the failure
 of the second thermocouples. Thus, the process can be run longer, and the
 shut-down and work-over of the gasifier can be planned in advance, without
 need for an emergency shut down. While the accuracy provided by the second
 thermocouple is not as good as the first thermocouple, the difference does
 not pose a problem for process control as the readings for the second
 thermocouple may be corrected based on data gathered prior to the failure
 of the first thermocouple.
 In another embodiment of the invention, there can be one or more other
 means of measuring gasifier temperature, including but not limited to
 traditional thermocouples in protective sheaths and optionally thermowells
 located in holes extending through the hotface brick, said sheaths being
 of any refractory materials mention or of materials subsequently found
 suitable. The convergence of the temperature recorded by the thermocouple
 located behind the hotface brick with the temperature of the thermocouple
 more directly exposed to the gasifier environment can be used to evaluate
 the condition of the hotface brick. For example, if the thermocouples
 behind the hotface brick that normally read 200.degree. F. (110.degree.
 C.) lower than the thermocouples more completely exposed to the gasifier
 interior get closer, for example to reading 100.degree. F. (55.degree. C.)
 lower than the thermocouples more completely exposed to the gasifier
 interior, than this is evidence of thinning of the layer of hotface brick.
 If the two measurements read the same, this is evidence of a substantial
 breach of the hotface brick. Finally, if the thermocouple ceases operation
 due to slag attack, this is evidence of breach of the hotface brick by
 slag at least to the depth of the hotface brick between the thermocouple
 and the gasifier interior. Knowledge of the failure of the hotface brick
 before the problem becomes acute can result in a more orderly shutdown and
 time to prepare for maintenance during the shutdown.