NON-LUBRICATING FLUID PUMPING SYSTEM

Abstract

One or more techniques and/or systems are disclosed for a pump technology that provides for more effective and efficient transfer of liquids, such as glycol products, in a glycol dehydration system. Such a technology can comprise a type of external gear pump that can effectively handle harsh conditions associated with glycol dehydration system at high pressures, while providing for longer pump life, effective operations at higher temperatures, and operations that account for thermal shock; with improved sealing capability, in a cost-effective system. An example pump may comprise hardened internal components, improved clearances, a jacket to mitigate thermal shock, and/or a thermal shock plate to mitigate thermal shock.

Description

RELATED APPLICATION DATA

This application claims benefit of U.S. Provisional Application No. 62/727,088 filed Sep. 5, 2018, which is incorporated herein by reference.

BACKGROUND

Extracted natural gas is typically saturated with water, such as water vapor, particularly when extracted from an underground source. Before being commercially marketed, the water is removed from the natural gas using a dehydration process. Commonly, glycol products are used in the dehydration process. Glycol is a liquid desiccant used in a glycol dehydration system for the removal of water from natural gas (NG) and natural gas liquids (NGL). Common types of glycols used include triethylene glycol (TEG), diethylene glycol (DEG), ethylene glycol (MEG), and tetraethylene glycol (TREG). A glycol dehydration system can use a pump for pumping the glycol through the system. Such pumps are subjected to operational conditions that often lead to short pump life, sensitivity to thermal shock, temperature limits of existing pumps, and leakage issues.

SUMMARY

This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key factors or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.

One or more techniques and systems are described herein for a pump technology that provides for more effective and efficient transfer of liquids, such as glycol products, in a glycol dehydration system. Such a technology can comprise a type of external gear pump that can effectively handle harsh conditions associated with glycol dehydration system at high pressures, while providing for longer pump life, effective operations at higher temperatures, and operations that account for thermal shock; with improved sealing capability, in a cost-effective system. In one implementation, a pump for pumping non-lubricating fluids at elevated temperatures may comprise an internal pump chamber comprising a first material. Further, the pump may comprise a driver shaft that provides rotational power to the pump; and a driven shaft that rotates as a result of the rotational power from the driver shaft. Additionally, the example, pump can comprise a first external gear disposed on the driver shaft in the internal pump chamber; and a second external gear disposed on the driven shaft in the internal pump chamber. The first external gear and the second external gear may comprise a second material, different than the first material. The first gear and second gear may be disposed in an intermeshing engagement that drives fluid through the internal pump chamber under the rotational power. The example pump may also comprise a head assembly disposed an end of the first shaft and second shaft. The first material and the second material may be rated to 350° F. and may be resistant to thermal shock.

To the accomplishment of the foregoing and related ends, the following description and annexed drawings set forth certain illustrative aspects and implementations. These are indicative of but a few of the various ways in which one or more aspects may be employed. Other aspects, advantages and novel features of the disclosure will become apparent from the following detailed description when considered in conjunction with the annexed drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A, 1B, and 1C are component diagram illustrating one implementation of an example pump for pumping glycol.

FIGS. 2A, 2B, and 2C are component diagram illustrating another implementation of an example pump.

FIGS. 3A, 3B, and 3C are component diagram illustrating another implementation of an example pump.

FIGS. 4A, 4B, and 4C are component diagram illustrating another implementation of an example pump.

DETAILED DESCRIPTION

The claimed subject matter is now described with reference to the drawings, wherein like reference numerals are generally used to refer to like elements throughout. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the claimed subject matter. It may be evident, however, that the claimed subject matter may be practiced without these specific details. In other instances, structures and devices are shown in block diagram form in order to facilitate describing the claimed subject matter.

Pumping glycol in a glycol dehydration system for natural gas has three common challenges: high temperature operation (e.g., can be approximately 200 Deg. F, or from about 175 to 225 Deg. F, but typically from about 140-160 Deg. F), at high pressures (e.g., up to 1500 psi), with a low lubricity liquid (e.g., glycol), with the potential for abrasives (e.g., sand, silt, etc.). Further, common operational conditions (e.g., cold climates) may have the pumps subjected to thermal shock at start-up, which may utilize a specialized start-up procedure. Such challenges may result in significant limitations in conventional pumps. For example, in a conventional pump, start-up processes may limit temperature ramp up to increments of 5° F. or less to prevent lockup due to thermal shock. In addition, lockups and thermal shock incurred by conventional pumps may degrade the pump and lead to limited pump life (e.g., less than a month in some environments).

As an example, a glycol pump is often used in a glycol dehydration system, where it may pump hot lean glycol into a glycol contactor, where water is stripped from the extracted natural gas. In this example, the lean glycol (e.g., substantially water fee, such as >99% purity) can be fed into the top of a glycol contactor. The contactor is used to place the glycol in contact with the “wet” natural gas; and through an absorption process, the glycol strips the water from the “wet” natural gas. The rich glycol (e.g., with the absorbed water) exits the contactor at the bottom, and the “dry” natural gas exits the contactor at the top. The rich glycol can be fed into a flash component and glycol regenerator, which removes hydrocarbons and water, resulting in lean glycol at an elevated temperature. The lean and hot glycol can then be pumped by the glycol pump back to the contactor. In one implementation, a heat exchanger may be used to reduce the temperature of the glycol, for example, down to a range of approximately 140-160 Deg. F. In one aspect, an external (e.g., spur) gear pump may be designed that provides for an extended pump life, and which can potentially handle thermal shock at startup. In one implementation, in this aspect, ways to address the challenges associated with this type of pump can include: hardening of faces, such as using nitrocarburizing (e.g., Vitek), anneal hardening, or thin dense chrome (e.g., Armoloy), or other; the use of self-lubricating bushings (e.g., DU bushing); adjusting clearances to mitigate thermal shock; the use of thermal jacketing, or heating (e.g., electrically) the pump to mitigate the thermal shock; the use of a mechanical seal to improve sealing capability; the use of a thermal shock plate to allow for thermal shock; and/or the use of silicon carbide bushings with a hardened or coated shaft to better handle abrasives. As one example, in this aspect, the pump technology described herein can be used to pump hot Triethylene glycol (TEG) for natural gas dehydration. A long felt need in the market was identified by users of such systems, used for pipeline injection, and with those involved in natural gas dehydration. Existing users of these systems are unhappy with current products available in the market, having including: short pump life, sensitivity to thermal shock, temperature limits of existing pumps, and leakage issues.

In the following example implementations, individual component's thermal expansion rates and material strengths were considered. Deliberate selection of materials that demonstrated controlled rates of the thermal expansion. Further, innovative external gear pump improvements offer significant advantages over conventional pumps. Such improvements may include without limitation, for example, reduced leakage, increased resistance to thermal shock and increased pump lifetimes in even challenging environments (e.g., on the order of years). Further, start-up processes may be increased from increments of 5° F. in conventional pumps to 100-150° F. or even eliminated.

There are several implementations described herein, which may be used for this type of application. In one or more of these implementations, a mechanical seal can be used to mitigate leakage of the pumped fluid (e.g., hot TEG). Further, in one or more of these implementations, the materials of construction used in the pump can be rated to 350 deg-F., in order to meet the conditions of desired operation. As stated earlier, these designs may provide the following advantages, for example: increased pump life; simplified start-up with thermal shock; improved performance at extreme application temperatures; and more reliable sealing solution. The improved material of construction and internal component clearances can also provide for operation that is more reliable and improved operational life.

In one implementation, a pump can be constructed using ductile iron for a base material, steel gears, self-lubricating bushings, and a hardened surface on the head and bracket. Further, in this implementation, tight end clearances on the shaft(s) can be used to increase the turn-up/turn-down ratio of the pump. In a further example, tight clearances may be the controlled running clearances between the gears and other pump components. The amount of clearance designed into a pump varies depending on gear diameter and overall gear length. In a specific, non-limiting example, a tight clearance may be about 1% when comparing clearance to diameter (e.g., the running clearance on the gears may be controlled to a tolerance of <0.003″±0.0002″ for a particular implementation). In further implementations, depending on the technology that is implemented, the running clearances can effectively be zero in a pressure-balance plate designed hydraulic positive displacement pump to about 0.125″ on a centrifugal pump. In other implementations, tolerances may be measured from the end of the gear to the bracket of the housing and/or radially from the tips of the teeth of the gears to the housing. This feature may also allow the pump to run more efficiently at operational temperature.

Adjustments may be made to either increase or decrease the running clearance to better serve a particular application. But simple variations may result in pumps with increased end clearance that sacrifice efficiency and limit the overall ability to generate flow and overcome system pressures. In effect, such conventionally built pumps will cease to function.

In another implementation, a pump can also be constructed using ductile iron for a base material, steel gears, self-lubricating bushings, and a hardened surface on the head and bracket. Further, additional running clearance may be used at various portions (e.g., end clearance of the gears, and/or tips of the gears, shaft(s), etc.) to improve thermal shock performance, for example, by allowing for expansion and contraction of some components during cold startup and operating at temperature.

Specifically, in an example glycol application (e.g., TEG), one obstacle is the potential of the pump to be subjected to large temperature spikes or thermal shocks. The rapid heating of the pump causes the internal components to expand. Because the individual components are generally different materials, they may expand at different rates and tightly controlled tolerances are eliminated which causes the pump to lock up. To counter this, the implementations described herein establish a balance of thermal shock capability while maintaining performance. Depending on the gear diameter and length, the amount of additional end clearance varies and may be an additional increase in a range of about 15-25% additional spacing to balance thermal shock capability while maintaining performance. In a non-limiting example, a 15-25% increase may be 0.0005″ to 0.001″ from a conventional pump. In other implementations, tolerances may be measured from the end of the gear to the bracket of the housing and/or radially from the tips of the teeth of the gears to the housing.

In another implementation, the bracket and casing faces can be subjected to increased hardening to improve the abrasive resistance of these components. As one example, the hardening may utilize a dense chromium process for metals, such as Armoloy. In this implementation, the pump can also be constructed using ductile iron for a base material, steel gears, self-lubricating bushings, and a hardened surface on the head and bracket.

In another implementation, the pump can comprise a jacketing system that allows the pump to be “warmed” prior to startup, for example, to make the startup procedure easier. As an example, a jacketing system can comprise thermal insulation, conduits used to distribute warming fluids, and/or electrical heating elements for warming the pump.

In another implementation, the pump can comprise a thermal shock plate proximate the cavity in the pump. As an example, the thermal shock plate may allow the pumping cavity to expand during thermal shock and shrink during steady state operation (e.g., at operational temperature). That is, a thermal shock plate, for example a variable end plate solution, may be configured such that conventional end clearances may be used in conjunction with the thermal shock plate allowing for the sudden thermal expansion (of the gears for example) by providing a void for the plate to be pushed or expand into. As an example, the thermal shock plate may be different than a typical pressure balance plate in that it may not force itself against the gears with increasing differential pressure. In one implementation, the thermal shock plate and mating components can be machined to allow the thermal shock plate to expand and shrink the pumping cavity to a predetermined size, which may provide desired running clearances for the gears and prolonging operational life of the pump.

FIGS. 1-4 are component diagrams illustrating various implementations of pumps 100, 200, 300, 400, that may comprise one or more portions of one or more systems described herein for pumping glycol. FIGS. 1A, 1B, and 1C illustrate one implementation of a pump 100 in various views (front, side, cut-away). In this implementation, the pump 100 can comprise a driver shaft 102 and a driven shaft 104. As an example, the driver shaft 102 can be coupled to (e.g., either directly or indirectly) some type of prime mover (e.g., motor or the like) that applies rotary power to the driver shaft 102, to rotate the shaft. In this example, the driven shaft 104 rotates as a result of the rotation of the driver shaft 102, and the intermeshing of gears between the two shafts.

Further, the example pump 100 can comprise pump housing 106, housing the internal workings of the pump 100; and a bracket and bushing assembly 108. In one examples, an innovative bracket can be used to hold the seal holder, and for shaft support, and support of the bushings. For example, the same bracket can be utilized while a different seal can be introduced for various application conditions. Further, utilizing this innovative bracket design, additional gear sections can be stacked with a longer drive shaft to add more bearings to support the shaft and mitigate and increase in loads on the bearings. This allows additional gear sections to be added to increase flow rate, without increasing the size (e.g., diameter) of the pump, which would occur in an existing system that merely increase the gear size. This allows for maintaining pressure ratings at an increased flow rate.

In FIGS. 1A, 1B, and 1C, the example pump 100 can comprise a gear assembly 110. The gear assembly 110 can comprise a series of gears, such as a first gear 112 and a second gear 114, respectively coupled to their associated shafts 102, 104. For example, the gears 112, 114 can be arranged in an intermeshing disposition with each other. In this example, rotation of the driver shaft 102 results in rotation of the first gear 112, which results in rotation of the second gear 114 and the driven shaft 104. As an example, the rotation of the intermeshing gears create expanding volume on the inlet side of the pump, and liquid flows into the internal pump cavity 120 and is trapped by the gear teeth as they rotate. As the liquid travels around the internal pump cavity 120 in the pockets between the teeth and the walls of the cavity, the meshing of the gears forces liquid through the outlet port.

Additionally, the example pump 100 can comprise a seal 116. For example, the seal 116 may be used mitigate leakage of fluid from the internal pump cavity 120 to outside of the pump, such as using some type of mechanical seal. The example pump 100 can comprise a head and bushing assembly 118. As an example, an innovative head design may allow the heads to be rotated without changing the bracket and casings. For example, this allows a user to rotate the head to provide for either clockwise (CW) or counter-clockwise (CCW) rotation in the same pump. Visual indicators may be provided to allow the user to set up the pump in the desired CW or CCW rotation. Further, this innovative design allows the designer of the pump installation to place the pump system in an appropriate position for the site situation. For example, the user can merely disassemble the pump and set the way that is appropriate for the situation, without replacing additional parts in the pump.

Further, in one aspect, an innovative bracket design may allow for multiple mechanical seal options with a single bracket, which can allow end users to choose between a standard component seal, a balanced component seal, or a cartridge seal with provisions for leak detection systems. Additionally, in this aspect, gear sections can be added to the pump to increase the flow rate while maintaining the original pressure rating. For example, being able to add gear sections is like having two, three or more pumps, but with only one seal and one prime mover. Machining on the separation plates and heads can also be provided to allow for the same parts to be flipped to achieve a CW or CCW build.

In another example, the innovative bracket can be used to hold the seal holder, and for shaft support. For example, the same bracket can be utilized while a different seal can be introduced for various application conditions. Further, utilizing this innovative bracket design, additional gear sections can be stacked with a longer drive shaft to add more bearings to support the shaft and mitigate an increase in loads on the bearings. This allows additional gear sections to be added to increase flow rate, without increasing the size (e.g., diameter) of the pump, which would occur in an existing system that merely increase the gear size. This allows for maintaining pressure ratings at increased flow rates.

As one example, as illustrated in the implementation of the pump 100, tighter clearances may be utilized. In this example, the tighter internal component clearances may allow for improved function for the operation, and can also provide for operation that is more reliable and improved operational life. In one example, the tighter clearances may be provided at the end of the gear(s), such as between the gear end(s) and the head assembly 118, and/or between the gears 112, 114 and the casing 110. This may be used to increase the turn-up/turn-down ratio of the pump.

The example pump system can comprise improved material construction that provides for improved operation, less maintenance, longer operational life, and lower overall cost. For example, the improved materials can comprise harder gears and gear teeth, such as hardened steel, steel alloys, and other metals that resist abrasion and other damage. In one implementation, one or more components can be Vitek hardened to increase wear resistance. By way of nonlimiting example, one of the improved materials may be a powdered metal described in standard FN-0208-155HT from MPIF Standard 35. In another non-limiting implementation, the improved material may be an alloy steel comprising an AISI 8620 base material with a carbon nitrated heat-treated steel layer over the base material. Further, the pump parts, including the gears, gear teeth, heads, casings, drive shaft, seal, bearings, and bushings can be formed with tighter tolerances (e.g., gaps) than previously found in these types of pumps. The improved tolerances and materials can help provide improved pressure ratings, improved use with non-lubricating fluids, and improved overall operational life.

FIGS. 2A, 2B, and 2C illustrate another implementation of a pump 200 in various views (front, side, cut-away). In this implementation, the example pump 200 can also comprise the various components illustrated and identified in FIG. 1, including: the driver shaft; driven shaft; pump housing; bracket and bushing assembly; gear assembly; 1^st and 2^nd gears; seal; head and bushing assembly, and internal pump cavity. Further, in this implementation, the example pump 200 can comprise a separation plate with a jacketed head assembly 222. As illustrated, the separation plate 222 can be disposed between the bracket and bushing assembly and a head assembly. In one example, the separation plate with a jacketed head assembly 222 may be used to provide pre-startup warming to mitigate thermal shock associated with use of the pump in cold conditions.

FIGS. 3A, 3B, and 3C illustrate another implementation of a pump 300 in various views (front, side, cut-away). In this implementation, the example pump 300 can also comprise a thermal shock plate 330. For example, the thermal shock plate 330 can be placed next to the internal pump cavity (e.g., 120). In this example, the thermal shock plate 330 may allow the pumping cavity to expand during thermal shock and shrink to a predetermined size during steady state operation (e.g., at operational temperature). In this way, the effects of thermal shock on the operation of the pump can be mitigated.

FIGS. 4A, 4B, and 4C illustrate another implementation of a pump 400 in various views (front, side, cut-away). In this implementation, the example pump 400 can also comprise additional clearance 440. As an example, the additional clearance can also help mitigate thermal shock, as it can provide additional room for expansion or contraction of the components of the pump. Further, the example pump 400 can comprise a foot 450, which may be used to secure the pump 400 to a set position, such as in a glycol dehydration system.

The word “exemplary” is used herein to mean serving as an example, instance or illustration. Any aspect or design described herein as “exemplary” is not necessarily to be construed as advantageous over other aspects or designs. Rather, use of the word exemplary is intended to present concepts in a concrete fashion. As used in this application, the term “or” is intended to mean an inclusive “or” rather than an exclusive “or.” That is, unless specified otherwise, or clear from context, “X employs A or B” is intended to mean any of the natural inclusive permutations. That is, if X employs A; X employs B; or X employs both A and B, then “X employs A or B” is satisfied under any of the foregoing instances. Further, At least one of A and B and/or the like generally means A or B or both A and B. In addition, the articles “a” and “an” as used in this application and the appended claims may generally be construed to mean “one or more” unless specified otherwise or clear from context to be directed to a singular form.

Although the subject matter has been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims.

Also, although the disclosure has been shown and described with respect to one or more implementations, equivalent alterations and modifications will occur to others skilled in the art based upon a reading and understanding of this specification and the annexed drawings. The disclosure includes all such modifications and alterations and is limited only by the scope of the following claims. In particular regard to the various functions performed by the above described components (e.g., elements, resources, etc.), the terms used to describe such components are intended to correspond, unless otherwise indicated, to any component which performs the specified function of the described component (e.g., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary implementations of the disclosure. In addition, while a particular feature of the disclosure may have been disclosed with respect to only one of several implementations, such feature may be combined with one or more other features of the other implementations as may be desired and advantageous for any given or particular application. Furthermore, to the extent that the terms “includes,” “having,” “has,” “with,” or variants thereof are used in either the detailed description or the claims, such terms are intended to be inclusive in a manner similar to the term “comprising.”

The implementations have been described, hereinabove. It will be apparent to those skilled in the art that the above methods and apparatuses may incorporate changes and modifications without departing from the general scope of this invention. It is intended to include all such modifications and alterations in so far as they come within the scope of the appended claims or the equivalents thereof.

Claims

1. A pump for pumping non-lubricating fluids, comprising:

an internal pump chamber comprising a first material;

a driver shaft that provides rotational power to the pump;

a driven shaft that rotates as a result of the rotational power from the driver shaft;

a first external gear disposed on the driver shaft in the internal pump chamber, the first external gear comprising a second material;

a second external gear disposed on the driven shaft in the internal pump chamber, the second external gear comprising the second material, the first gear and the second gear being disposed in an intermeshing engagement that drives fluid through the internal pump chamber under the rotational power; and

a head assembly disposed at an end of the driver shaft and the driven shaft;

wherein the first material is different than the second material, and the first material and the second material are rated to 350° F. and are resistant to thermal shock.

2. The pump of claim 1, wherein the fluid comprises glycol.

3. The pump of claim 1, wherein the first material comprises ductile iron and the second material comprises steel, hardened steel, or a steel alloy.

4. The pump of claim 1, further comprising self-lubricating bushings operably connected to the driver shaft and the driven shaft.

5. The pump of claim 1, further comprising a bracket assembly disposed at an opposite end of the driver shaft and the driven shaft from the head assembly.

6. The pump of claim 5, wherein the head assembly and the bracket assembly comprise a hardened surface layer, the hardened surface layer being rated to 350° F. and resistant to thermal shock.

7. The pump of claim 6, wherein the hardened surface comprises a surface hardened by a dense chromium process.

8. The pump of claim 1, comprising a thermal shock plate disposed adjacent the internal pump chamber that allows the internal pump chamber to expand and contract to mitigate thermal shock at startup, the thermal shock plate being rated to 350° F. and resistant to thermal shock.

9. The pump of claim 1, comprising a clearance between the end of the driver shaft and the head assembly, and between the end of the driven shaft and the head assembly, each respective clearance configured such that the end of the driver shaft and the head assembly and the end of the driven shaft and the head assembly are substantially sealed from leakage.

10. A pump for pumping non-lubricating fluids, comprising:

an internal pump chamber;

a driver shaft that provides rotational power to the pump;

a driven shaft that rotates as a result of the rotational power from the driver shaft;

a first external gear disposed on the driver shaft in the internal pump chamber;

a second external gear disposed on the driven shaft in the internal pump chamber, the first gear and the second gear being disposed in an intermeshing engagement that drives fluid through the internal pump chamber under the rotational power;

a head assembly disposed at an end of the first shaft and second shaft; and

a thermal shock plate disposed adjacent the internal pump chamber that allows the internal pump chamber to expand and contract to mitigate thermal shock at startup, the thermal shock plate being rated to 350° F. and resistant to thermal shock.

11. The pump of claim 10, wherein:

the internal pump chamber comprises a first material; and

the first external gear and the second external gear each comprise a second material, the first material being different than the second material, and the first material and the second material being rated to 350° F. and are resistant to thermal shock.

12. The pump of claim 11, wherein the first material comprises ductile iron and the second material comprises steel, hardened steel, or a steel alloy.

13. The pump of claim 11, further comprising a bracket assembly disposed at an opposite end of the first shaft and the second shaft from the head assembly.

14. The pump of claim 13, wherein the head assembly and the bracket assembly comprise a hardened surface layer, the hardened surface layer being rated to 350° F. and resistant to thermal shock.

15. A pump for pumping non-lubricating fluids, comprising:

an internal pump chamber;

a driver shaft that provides rotational power to the pump;

a driven shaft that rotates as a result of the rotational power from the driver shaft;

a first external gear disposed on the driver shaft in the internal pump chamber;

a second external gear disposed on the driven shaft in the internal pump chamber, the first gear and the second gear being disposed in an intermeshing engagement that drives fluid through the internal pump chamber under the rotational power;

a head assembly disposed at an end of the first shaft and second shaft; and

an area of additional clearance between the end of the driver shaft and the head assembly, and between the end of the driven shaft and the head assembly configured such that the additional clearance absorbs thermal shock at startup of the pump.

16. The pump of claim 15, further comprising a bracket assembly disposed at an opposite end of the first shaft and the second shaft from the head assembly.

17. The pump of claim 16, wherein the head assembly and the bracket assembly comprise a hardened surface layer, the hardened surface layer being rated to 350° F. and resistant to thermal shock.

18. The pump of claim 15, wherein:

the internal pump chamber comprises a first material; and

the first external gear and the second external gear each comprise a second material, the first material being different than the second material, and the first material and the second material are rated to 350° F. and are resistant to thermal shock.

19. The pump of claim 18, wherein the first material comprises ductile iron and the second material comprises steel, hardened steel, or a steel alloy.

20. The pump of claim 15, further comprising a thermal shock plate disposed adjacent the internal pump chamber that allows the internal pump chamber to expand and contract to mitigate thermal shock at startup, the thermal shock plate being rated to 350° F. and resistant to thermal shock.