WO2010064006A1

WO2010064006A1 - Systems and methods for managing reactor transients

Info

Publication number: WO2010064006A1
Application number: PCT/GB2009/002804
Authority: WO
Inventors: Gillian Kerr; Robert John O'brien
Original assignee: Invista Technologies S.A.R.L.
Priority date: 2008-12-02
Filing date: 2009-12-02
Publication date: 2010-06-10
Also published as: CN102239000B; CN102239000A

Abstract

The present invention relates to a system having an oxidation reactor configured to oxidize an aromatic feedstock to produce an aromatic carboxylic acid; and a machine train that provides compressed air to the reactor, where the machine train includes a single-shaft air compressor.

Description

SYSTEMS AND METHODS FOR MANAGING REACTOR TRANSIENTS

BACKGROUND

The production of aromatic carboxylic acids, such as terephthalic acid (TA), typically involves the liquid-phase oxidation of an aromatic feedstock compound, such as paraxylene, using molecular oxygen in a solvent, usually in the presence of a catalyst that incorporates a promoter. In general, the solvent, molecular oxygen, feedstock, and catalyst are continuously fed into an oxidation reactor at an elevated temperature and pressure. Feedstock oxidation within the reactor produces a high- pressure gaseous stream or "off-gas" that typically comprises nitrogen, unreacted oxygen, carbon dioxide, carbon monoxide and, where bromine is used as a promoter, methyl bromide. Because the reaction is exothermic, the solvent is often allowed to vaporize to control the reaction temperature. Therefore, the off-gas can further comprise vaporized solvent.

The off-gas from the reactor contains a significant amount of energy, which can be recovered to reduce the total energy consumed during production and at least partially offset the cost of obtaining the high temperatures and pressures required by the oxidation reactor. Often times, the off-gas is directed to an expander that drives a compressor, which feeds pressurized air to the reactor. Steam raised while condensing the gaseous stream that is not required elsewhere can be directed to a turbine that is also used to drive the compressor.

When stable operating conditions are not maintained in the oxidation reactor, transient conditions, or "transients," occur and air feed to the reactor must be cut, the off-gas from the reactor quickly reduces to zero and steam is no longer raised by the condensers for the turbine. In such cases, the machine train, which includes the turbine, the expander, and the compressor, must either be shut down or supplemental energy must be applied to keep the machine train online. Because of the time and cost associated with bringing the machine train back online after shut down, it is generally preferable to keep the machine train online while the issue that caused the transient is being resolved. Unfortunately, the costs of keeping the machine train online are undesirably high due to the substantial amounts of supplemental energy, in the form of high pressure steam and/or electricity from an auxiliary source, that are required to keep the machine train running at its normal operating speed.

In view of the above, it can be appreciated that it would be desirable to have a system and method with which reactor transients can be managed such that the machine train can be kept online but with less supplemental energy from an auxiliary source.

BRIEF DESCRIPTION OF THE FIGURE

The components in the drawing are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the present disclosure. In the drawing, like reference numerals designate corresponding parts throughout the several views.

FIG. 1 is a schematic view of an embodiment of a system for producing an aromatic carboxylic acid. DETAILED DESCRIPTION

Introduction

As described above, it is generally undesirable to shut down a machine train in an aromatic carboxylic acid production plant when a reactor transient occurs due to the time and cost associated with bringing the machine train back online once the transient has been resolved. Furthermore, the cost of maintaining the machine train at its normal operating conditions during that duration are undesirably high due to the substantial amounts of supplemental energy that are required. As described herein, however, significant energy and therefore cost savings can be realized by modifying the machine train configuration so that it can be safely operated at reduced speeds during reactor transients.

In some embodiments, an axial or radial single-shaft compressor can be used in the machine train of an aromatic carboxylic acid production plant that, unlike the integrally-geared compressors typically used in such plants, can be safely operated over a wide range of speeds. By way of example, the machine train speed can be reduced to the point at which the supplemental steam and/or electric power needed to operate the machine train while the reactor is offline is reduced to a third of what would normally be required. In addition to reducing energy requirements during transients, the use of a single-shaft compressor and the reduced machine train operating speeds it facilitates enables the use of smaller boilers within the plant, thereby potentially reducing plant equipment costs.

In some embodiments the plant incorporates an air bypass route that extends from the compressor to the expander. When a transient occurs, a control system opens the bypass route to deliver compressed air to the expander, and deliberately reduces the train speed to a setpoint in the range of approximately 70% to 95% of normal operating speed. The particular setpoint selected depends on machine configurations for both thermodynamic characteristics and mechanical requirements, such as torsional excitation, impeller resonance, blade pass interference, and lateral critical speeds. Regardless, because the expander is maintained at an elevated temperature due to the redirection of compressed air from the compressor, the machine train can be quickly ramped back up to normal operating speed once the transient condition has been resolved.

Various embodiments of systems and methods are described in the following discussion. Although particular embodiments are described, the disclosed systems and methods are not limited to those particular embodiments. Instead, the described embodiments are mere example implementations of the disclosed systems and methods.

Example System and Normal Operation

Referring now to FIG. 1 , illustrated is an example system 10 for producing aromatic carboxylic acid by the exothermic, liquid-phase oxidation of an aromatic feedstock compound. In some embodiments, the system 10 comprises part of a larger aromatic carboxylic acid production plant including other components of which are not illustrated in FIG. 1.

As indicated in FIG. 1 , the system 10 comprises a reaction system 12 that includes an oxidation reactor 14 in which the aromatic feedstock can be oxidized to produce the aromatic carboxylic acid. More particularly, an aromatic carboxylic acid can be produced within the reactor 14 through the high pressure, exothermic oxidation of a suitable aromatic feedstock compound in a liquid-phase reaction using an oxidant, an oxidation solvent, a catalyst, and a promoter.

The aromatic feedstock compound used can be any aromatic compound that has oxidizable substituents that can be oxidized to a carboxylic acid group. For example, the oxidizable substituent can be an alkyl group such as a methyl, ethyl, or isopropyl group. The substituent can also be a partially-oxidized alkyl group, such as an alcohol group, aldehyde group, or ketone group. The aromatic portion of the aromatic feedstock compound can be a benzene nucleus or it can be bi- or polycyclic, for example a naphthalene nucleus. The number of oxidizable substituents on the aromatic portion of the aromatic feedstock compound can be equal to the number of sites available on the aromatic portion of the aromatic feedstock compound, but is generally fewer, for example 1 to about 4, suitably 2 or 3. Examples of suitable aromatic feedstock compounds include toluene, ethylbenzene, oxylene, metaxylene, paraxylene, 1-formyl-4-methylbenzene, 1-hydroxymethyl-4- methylbenzene, 1 ,2,4-trimethylbenzene, 1-formyl-2,4-dimethylbenzene, 1 ,2,4,5- tetramethylbenzene, alkyl, hydroxymethyl, formyl, and acyl substituted naphthalene compounds such as 2,6- and 2,7-dimethylnaphthalene, 2-acyl-6-methylnaphthalene, 2-formyl-6-methylnaphthalene, 2-methyl-6-ethylnaphthalene, 2,6-diethylnaphthalene, and the like. For the illustrative purposes of this disclosure, it is assumed that the aromatic feedback compound is paraxylene (PX) and it is used to produce terephthalic acid (TA). Molecular oxygen can be used as the oxidant. In some embodiments, air, which can be oxygen enriched or depleted, is a suitable source of molecular oxygen. In order to avoid the formation of explosive mixtures, the oxygen-containing gas fed to the oxidation reactor 14 provides an exhaust gas-vapor mixture containing from approximately 0.5 to approximately 8 volume percent oxygen (measured on a solvent-free basis). For example, a feed rate of the oxygen-containing gas sufficient to provide oxygen in the amount of from approximately 1.5 to approximately 2.8 moles per methyl group will provide approximately 0.5 to 8 volume percent of oxygen (measured on a solvent-free basis) in the overhead gas-vapor mixture.

The oxidation solvent can be a low molecular weight aliphatic monocarboxylic acid having approximately 2 to 6 carbon atoms, or mixtures thereof with water. In some embodiments, the solvent comprises an acetic acid or a mixture of an acetic acid and water.

Suitable catalysts include those heavy metals having an atomic number of approximately 21 to about 82 such as a mixture of cobalt and manganese, and suitable promoters include bromine promoter compounds such as hydrogen bromide, molecular bromine, and sodium bromide. The catalyst/promoter employed in producing crude terephthalic acid can, for example, comprise cobalt, manganese, and bromine components, and can additionally comprise accelerators. The ratio of cobalt (calculated as elemental cobalt) in the cobalt component of the catalyst-to- paraxylene in the liquid-phase oxidation can be in the range of about approximately 0.2 to 10 milligram atoms (mga) per gram mole of paraxylene. The ratio of manganese (calculated as elemental manganese) in the manganese component of the catalyst-to-cobalt (calculated as elemental cobalt) in the cobalt component of the catalyst in the liquid-phase oxidation can be in the range of about approximately 0.2 to 10 mga per mga of cobalt. The weight ratio of bromine (calculated as elemental bromine) in the bromine component of the catalyst-to-total cobalt and manganese (calculated as elemental cobalt and elemental manganese) in the cobalt and manganese components of the catalyst in the liquid-phase oxidation can be in the range of approximately 0.2 to 1.5 mga per mga of total cobalt and manganese.

Each of the cobalt and manganese components can be provided in any of its known ionic or combined forms that provide soluble forms of cobalt, manganese, and bromine in the solvent in the oxidation reactor 14. For example, when the solvent is an acetic acid medium, cobalt and/or manganese carbonate, acetate tetrahydrate, and/or bromine can be employed. The 0.2:1.0 to 1.5:1.0 bromine-to-total cobalt and manganese milligram atom ratio can be provided by a suitable source of bromine. Such bromine sources can include elemental bromine (Br₂), ionic bromine {for example HBr, NaBr, KBr, NH₄Br, etc.), or organic bromides that are known to provide bromide ions at the operating temperature of the oxidation (e.g., benzylbromide, mono- and di-bromoacetic acid, bromoacetyl bromide, tetrabromoethane, ethylene- di-bromide, etc.). The total bromine in molecular bromine and ionic bromide is used to determine satisfaction of the elemental bromine-to-total cobalt and manganese milligram atom ratio of 0.2:1.0 to 1.5:1.0. The bromine ion released from the organic bromides at the oxidation operating conditions can be readily determined by known analytical means. For the oxidation of paraxylene to terephthalic acid, the minimum pressure at which the oxidation reactor 14 is maintained is typically that pressure that will maintain a substantial liquid phase of the paraxylene and the solvent. When the solvent is an acetic acid-water mixture, suitable reaction gauge pressures in the oxidation reactor 14 can be in the range of approximately 0 kg/cm² to 35 kg/cm², and typically are in the range of approximately 10 kg/cm² to 20 kg/cm². The temperature range within the oxidation reactor can be, for example, approximately 120⁰C to 250⁰C. By way of example, the solvent residence time in the reactor 14 can be approximately 20 to 150 minutes, for example approximately 30 to 120 minutes.

The oxidation reactor 14 typically comprises a vessel that is constructed of or lined with a corrosion-resistant material, such as titanium or glass. Because the oxidation reaction is conducted at an elevated pressure, the reactor 14 is constructed to withstand the high pressures used for the oxidation reaction. In addition, the reactor 14 can be equipped with one or more mechanical agitators (not shown). Crude terephthalic acid produced by the oxidation reaction leaves the reactor 14 along a outlet line 16 in the form of an oxidation reaction slurry that comprises a mixture of crude terephthalic acid, water, acetic acid, catalyst metals, oxidation reaction intermediates, and reaction byproducts. The slurry can then be processed using a variety of procedures and equipment (not shown) to produce purified terephthalic acid.

During the liquid-phase oxidation within the oxidation reactor 14, heat is produced. In view of the considerable amount of energy that is comprised by the reaction off-gas, steps are taken to recover at least a portion of that energy and use it within the plant. For instance, the off-gas can be used to raise various pressures of steam that can, for example, be used to drive and/or heat other components of the system 10. In the embodiment of FIG. 1 , the off-gas exits the oxidation reactor 14 and flows through a gas line 18 to a series of condensers 20, 22, and 24, which condense the off-gas and raise steam. In some embodiments, the first condenser 20 can produce low pressure steam at approximately 145°C and approximately 4.5 bar, the second condenser 22 can produce extra-low pressure steam at approximately 130⁰C and approximately 3 bar, and the condenser 24 can produce very-low pressure steam at approximately 100°C and approximately 1 bar.

In the embodiment of FIG. 1 , the steam from the first condenser 20 flows along steam lines 26 and 28 to various low pressure steam users within the plant. Examples of such users include reboilers and driers. Steam from the second condenser 22 can flow along steam line 30, through control valve 32, and into a turbine 34 that is coupled to an electric generator 36 with a shaft 38. Therefore, steam raised using the second condenser 22 can be used to generate electricity, which can be used to drive various equipment of the plant. As shown in FIG. 1 , a further steam line 40 is connected to the exit of the turbine 34 and delivers the steam to a heat exchanger 42, which condenses the steam into condensate that is output along condensate line 44.

Additionally, a further steam line 50 also having a control valve 52 joins steam lines 26 and 30 to facilitate the delivery of steam from line 26 to line 30 for the purpose of driving the turbine 34. Furthermore, a steam line 54 having a control valve 56 extends from the steam line 26 to a further turbine 58 described below. Steam from the condenser 24 travels along a steam line 60 and is split into two paths, a first path 62 having a control valve 64 and leading to the turbine 58, and a second path 66 having a dump valve 68 and leading to a heat exchanger 70, which in an emergency condenses the steam into condensate that is output along condensate line 72. Exhaust steam from turbine 58 is passed to the heat exchanger 70, which condenses the steam into condensate that is output along condensate line 72.

As is further illustrated in FIG. 1 , the system 10 includes a control valve 76 that couples the steam line 26 to a steam line 78 along which auxiliary high pressure (HP) steam, for instance produced by one or more small package boilers of the plant (not shown), can be input into the system. As described below, that steam can be provided to the turbine 58 during reactor transients.

The turbine 58 comprises one component of a machine train that also includes an air compressor 80 and an expander 82. The turbine 58 is coupled to the air compressor 80 with a coupling 84, and the expander 82 is coupled to the compressor with a coupling 86. Both the turbine 58 and the expander 82 are used to drive the compressor 80, which draws in air along inlet line 88 and produces pressured air that can be supplied to the oxidation reactor 14 along air line 90. For reasons described below, the compressor 80 is an axial and/or radial single-shaft compressor, occasionally referred to as a "between-bearing" compressor, instead of a integrally- geared compressor typically used in TA plants, which typically comprise multiple shafts that operate at different speeds. By way of example, the compressor 80 supplies air to the reactor 14 at a temperature of approximately 150⁰C to 250°C and a pressure of approximately 6 to 25 bar. During normal operation, the expander 82 is the primary drive component for the compressor 80, with the remainder of the driving force being supplied by the turbine 58. Under normal operating conditions, the expander 82 obtains its energy from the reaction off-gas supplied through gas line 92 after the off-gas has passed through each of the condensers 20, 22, and 24.

When the off-gas passes through the condensers 20, 22, and 24, much of the organic materials within the off-gas condense, and that condensate can be returned to the oxidation reactor 14 after various processing. As a consequence of the heat transfer that occurs within the condensers 20, 22, and 24, the remaining off-gas can be relatively cold, but is still at relatively high pressure. By way of example, that off- gas has a temperature of approximately 40⁰C and a pressure of approximately 12 bar. Accordingly, the off-gas comprises substantial energy that can be put to use. While the off-gas could be sent directly to the expander 82, it is typical to first remove corrosive and/or combustible byproduct materials from the off-gas.

In the embodiment of FIG. 1 , a catalytic combustion unit (CCU) 100 is used to catalytically oxidize the off-gas into environmentally-compatible materials. An example of such a CCU is described in U.S. Pat. No. 5,961 ,942, which is hereby incorporated by reference. Such a unit 100 can reduce or eliminate through oxidation, any residual oxidation reaction solvent present in the off-gas, and can oxidize byproducts, such as methyl bromide. Prior to entering the CCU 100, the off- gas is heated using heat exchangers 96 and 98 to facilitate the oxidation reaction within the CCU. In some embodiments, heat exchanger 96 uses high pressure steam from the plant boiler to raise the temperature to approximately 200⁰C to 300°C. The off-gas then passes through the heat exchanger 98 and a gas line 99, and into the CCU 100 for oxidation. Fuel can be supplied to the CCU 100 via a fuel line 102 to assist in the reaction. The reaction within the CCU 100 produces further heat that can be transferred to the heat exchanger 98 by delivering the off-gas, now at a temperature of approximately 400⁰C to 510⁰C, through a further gas line 101 and back into the heat exchanger 98. That heat can then be transferred to the off-gas flowing toward the CCU 100.

After passing through the CCU 100 and the heat exchanger 98, the off-gas has, for example, a temperature of approximately 300°C to 400⁰C and a pressure of approximately 6 to 14 bar. The gas is then delivered to the expander 82 along a gas line 104 and is used to drive the expander 82, which in turn drives the compressor 80. The off-gas exits the expander 82 at or near atmospheric pressure and flows along gas line 106 to a scrubber 108, which removes any acidic and/or inorganic materials, such as bromine and hydrogen bromide, and then exhausts the gas into the atmosphere via gas line 110.

Further comprised by the system 10 of FIG. 1 is a blow-off line 112 and control valve 114 that are connected to the air line 90, and a bypass line 116 and control valve 118 that extend between the air line 90 and the gas line 92. As described below, those components are used when reactor transients occur that require the flow of compressed air to the reactor 14 to be shut off. Management of Reactor Transients

In certain circumstances, the oxidation reactor of an aromatic carboxylic acid production plant must be taken offline. One such circumstance is when the reactor is simply taken offline for cleaning or routine maintenance. In other circumstances, however, a condition arises that requires a reactor shut down. Such conditions are referred to as reactor transient conditions, or just transients. When a transient occurs, the reactor is shut down or "tripped" to avoid damage to equipment and/or harm to those that operate that equipment.

When an oxidation reactor is tripped, the supply of air to the reactor must be quickly shut off to reduce the risk of fire or explosion. In traditional plants, this is accomplished by immediately venting the air from the compressor to the atmosphere. Once compressed air is no longer provided to the reactor, however, the oxidation reaction ceases and the off-gas and steam produced by the reaction ceases to be produced. Without that off-gas and steam, the machine train loses its primary source of power and will slow down from its normal operating speed unless supplied with additional power. In conventional systems that employ integrally-geared compressors, such uncontrolled slowing from the normal operating speed can resuU in operation at a critical speed which can damage and even destroy the compressor within as little as 30 to 60 seconds.

In view of the damage that can occur due to uncontrolled machine train slowing, most conventional systems utilize supplemental energy to maintain the train at its normal speed. For instance, high pressure steam from a large boiler can.be provided to the machine train (e.g., a turbine of the train) and/or an electric motor can be powered to drive the train. Unfortunately, such solutions require substantial amounts of energy and, therefore, substantial cost. As described in the following, however, the amounts of supplemental energy and the associated costs can be significantly reduced by using the aforementioned single-shaft compressor 80 that, unlike integrally-geared compressors typically used in the industry, can be operated over a wide range of speeds without damage. For example, when the speed of the machine train is slowed in a controlled manner, the amount of supplemental steam required from a separate steam source, such as a plant boiler, can be significantly reduced. Because only a relatively small amount of supplemental steam is required in such circumstances, a small package boiler (e.g., having an approximate 70 te/hr capacity) is adequate to drive the machine train, thereby obviating the need to purchase and operate a high-capacity boiler.

Control of the system 10 in the manner described above will now be discussed with reference to FIG. 1. When a transient occurs and the oxidation reactor 14 is tripped, the control valve 76 associated with steam line 78 and the control valve 56 associated with steam line 54 are both opened to enable the flow of high pressure steam from a steam source, such as a plant boiler, to the turbine 58. By way of example, the steam is at a temperature of approximately 300°C and a pressure of approximately 80 bar and is let down to low pressure steam via control valve 76. That steam drives the turbine 58 to at least partially account for the loss of the steam provided from the condensers 20, 22 and 24 during normal system operation. At or near the same time, the control valve 118 of bypass line 116 is opened to divert the flow of compressed air from the oxidation reactor 14 to the expander 82, which normally operates using the reactor off-gas. By providing that air to the expander 82, the expander continues to be driven, albeit at a slower speed, and further is maintained at a relatively high temperature so that normal operation of the system 10 can be resumed relatively quickly. By way of example, the expander 82 can be operated at approximately 300⁰C during the reactor transient, which is only approximately 70⁰C cooler than during normal system operation. Notably, the blow- off valve 114 can also be opened, at least partially, so that a portion of the compressed air is vented to the atmosphere. Through careful selection of the amount of steam that is provided to the turbine 58 and the amount of compressed air that is provided to the expander 82, the machine train can be safely operated at approximately 70% to 95% its normal operating speed. In some embodiments, the steam and air flows are controlled by a central computer system (not shown) that controls the timing of actuation of all the implicated control valves, as well as the extent to which each open valve is opened.

Table I provides an indication of the advantageous results that the above- described control scheme can produce. Three systems are identified in the table, including an existing high-temperature expander system, an existing low-temperature expander system, and a high-temperature expander system in accordance with the present disclosure. In the existing high-temperature expander system, it is assumed that the expander is operated at approximately 450⁰C under normal operating conditions. For the existing low-temperature expander system, it is assumed that the expander is operated at approximately 190⁰C under normal operating conditions. Finally, for the disclosed high-temperature expander system, the expander is assumed to operate at approximately 370⁰C, as described above. Supplemental steam requirements for each of the start-up case, normal operating case, and reactor trip case are identified as to each system. In addition, the electricity loss is identified for each reactor trip case.

TABLE I

As can be appreciated from comparison of the existing low-temperature expander system and the disclosed high-temperature expander system, far less supplemental steam is required once a reactor trip occurs in the case of the disclosed high-temperature expander system. Specifically, while demand for supplemental steam increases from 105 te/hr during normal operation to 265 te/hr during a reactor trip in the existing low-temperature expander system, steam demand only increases from 80 te/hr during normal operation to 180 te/hr during a reactor trip in the disclosed high-pressure expander system. Therefore, far less additional steam is required during a reactor trip for the high-temperature expander system of the present disclosure.

Turning to the existing high-temperature expander system, although the amount of supplemental steam that is required when transitioning from normal operation to reactor trip operation is less for the existing high-temperature expander system than the disclosed high-temperature expander system, far less electricity is lost by the disclosed high-temperature expander system, and therefore far less electricity must be imported from an auxiliary source, thereby providing a net reduction in costs.

As can be appreciated from the foregoing disclosure, several advantages can be achieved when the disclosed system configuration and control scheme are used. First, by alternatively controlling the flow of steam and air within the system, the machine train can be controllably operated at a significantly reduced speed during reactor transients, which saves costs in terms of reduced supplemental steam and/or supplemental electricity requirements. Second, due to the use of a single-shaft compressor instead of an integrally-geared compressor, the reduced speed and attendant costs savings are achieved without the risk of damaging system components. Third, through the diversion and utilization of the compressed air from the compressor, relatively high temperature operation of the expander can be maintained during the transient such that the system can be ramped back up to normal operating conditions in a relatively short period of time. Furthermore, given that there is no motor generator included in the machine train, electrical faults that are common with such generators need not be accommodated.

Claims

CLAIMSClaimed are:

1. A system comprising: an oxidation reactor configured to oxidize an aromatic feedstock to produce an aromatic carboxylic acid; and a machine train that provides compressed air to the reactor, the machine train including a single-shaft air compressor.

2. The system of claim 1 , wherein the machine train further comprises an expander that drives the compressor during normal system operation and a bypass line along which compressed air from the air compressor can be diverted to an expander during oxidation reactor transients to both drive the expander and maintain the expander at an elevated temperature.

3. The system of claim 1, wherein the machine train is configured to be driven at approximately 70% to 95% of its normal operating speed during oxidation reactor transients.

4. The system of claim 1 , wherein the machine train further includes a turbine that drives the air compressor.

5. The system of claim 4, wherein the turbine is configured to receive steam from an auxiliary source during oxidation reactor transients to maintain operation of the machine train during the transients.

6. The system of claim 4, further comprising condensers through which off- gas from the oxidation reactor flow to generate steam that is provided to the turbine during normal system operation.

7. The system of claim 1 , wherein the machine train does not include a motor or a generator.

8. A method for managing oxidation reactor transients in an aromatic carboxylic acid production plant, the method comprising: forming a machine train within the plant comprising an air compressor, an expander, and a turbine; detecting an oxidation reactor transient; and responsive to the detected transient, operating the machine train at a reduced speed.

9. The method of claim 8, wherein operating the machine train at a reduced speed reduces the consumption of supplemental steam at the plant.

10. The method of claim 8, wherein operating the machine train at a reduced speed reduces the consumption of electricity at the plant, compared to a machine train with a motor.

11. The method of claim 8, wherein forming a machine train comprises forming a machine train having a single-shaft compressor.

12. The method of claim 11 , wherein operating the machine train comprises operating the machine train at approximately 70% to 95% normal operating speed.

13. The method of claim 8, further comprising, responsive to detection of the oxidation reactor transient, delivering steam from a plant boiler to the turbine to account for the loss of steam normally produced using the reactor off-gas.

14. The method of claim 8, further comprising, responsive to detection of the oxidation reactor transient, diverting compressed air from the air compressor to the expander to drive the expander and maintain the expander at an elevated temperature.