PROCESS AND APPARATUS FOR USING A WASTE HEAT STREAM IN AN AROMATICS COMPLEX

Abstract

The present invention relates to a process and apparatus for using a waste heat stream in an aromatics complex. More specifically, the present invention relates to a process and apparatus for using waste heat to drive multiple compressor services within an aromatics complex to achieve energy savings and provide low grade heat that is otherwise wasted.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority from Provisional Application No. 62/527,710 filed Jun. 30, 2017, the contents of which cited application are hereby incorporated by reference in its entirety.

FIELD

The present invention relates to a process and apparatus for using a waste heat stream in an aromatics complex. More specifically, the present invention relates to a process and apparatus for using waste heat to drive multiple compressor services within an aromatics complex to achieve energy savings and make use of low grade heat that is otherwise wasted.

BACKGROUND

In an Organic Rankine Cycle (ORC) system, process waste heat that is otherwise transferred in air and water coolers can be used to vaporize a low boiling refrigerant working fluid at moderate temperature and pressure, and energy from the vapor can be recovered. Typical organic rankine cycle (ORC) uses the working fluid to drive a turboexpander linked to a generator which delivers power to an electrical grid. The application of an ORC to recover waste heat in a refinery is typically a relatively low efficiency system with high capital cost, approximately 50% of which is related to the turbo-expander and generator.

A Rankine cycle is useful for generating power from a low or medium temperature heat source. A working fluid is evaporated, for example in an evaporator or boiler, upon exchanging heat with the source, and the vaporized fluid is then used in a turboexpander that drives an electrical generator or other load. Exhaust vapors from the turboexpander are condensed, and the resulting fluid may be recycled for heat exchange. An ORC uses an organic fluid as a working fluid. Known applications of ORC systems include generating power from geothermal heat sources, as described in U.S. Pat. No. 5,497,624 and U.S. Pat. No. 6,539,718. The use of an ORC in combination with fuel cell products and other forms of waste heat is described in US 2006/0010872, WO 2006/104490, and WO 2006/014609. Applications of an ORC involving solar energy and biomass are described in CN11055121, JP2003227315A2, INTERNATIONAL JOURNAL OF ENERGY RESEARCH, 28(11): 1003-1021 (2004), and ENERGY, 32(4): 371-377 (2007). The use of an ORC is also taught in U.S. Pat. No. 7,049,465, for improving energy recovery from exothermic reactions and particularly the liquid phase oxidation of paraxylene to terephthalic acid.

There is an ongoing need in the art for methods for recovering energy such as electricity from sources providing low grade heat that is otherwise wasted, especially those sources resulting from refinery and petrochemical plant operations. This need is particularly significant in view of the large quantities of low grade heat generated in these operations and the high energy and cost savings potentially realized from recovering even a fraction of this heat. The net generation of electricity is of significant benefit to refiners and petrochemical producers, due to reduced emissions of the combustion product CO₂ from materials (e.g., coal) used as a raw material in power plants.

SUMMARY

The proposed invention would significantly improve the economics by drastic reduction of the capital cost associated with the turboexpander and generator system by replacing it with a direct compressor driver system. Compressors are relatively high consumers of power in a refinery process unit, and they are typically driven by either steam turboexpanders or electric motors. The proposed invention seeks to replace the compressor power supply with power supplied by the organic working fluid. The compressor driver is a low cost replacement for the turboexpander and generator. The power saved in the compressor operation is equal to or greater than the power that would have otherwise been supplied to the grid.

Even energy efficient aromatics complexes may have a significant amount of low grade waste heat that that could be recovered for production of electricity using an organic Rankine cycle. This invention seeks to significantly improve the capital cost and payback. Such an energy recovery system could be applied to several different columns producing overhead energy used to drive both recycle gas compressors.

BRIEF DESCRIPTION OF THE DRAWING

The FIGURE illustrates a process and apparatus for using waste heat to drive multiple compressor services within an aromatics complex.

DETAILED DESCRIPTION

The following detailed description is merely exemplary in nature and is not intended to limit the application and uses of the embodiment described. Furthermore, there is no intention to be bound by any theory presented in the preceding background or the following detailed description.

The further description of the process of this invention is presented with reference to the FIGURE. The FIGURE is a simplified flow diagrams of a preferred embodiment of this invention and is not intended as an undue limitation on the generally broad scope of the description provided herein and the appended claims. Certain hardware such as valves, pumps, compressors, heat exchangers, instrumentation and controls, have been omitted as not essential to a clear understanding of the invention. The use and application of this hardware is well within the skill of the art.

The invention is associated with methods for generating electrical power from sources of low grade heat, particularly refining and petrochemical process streams, through the use of an Organic Rankine Cycle (ORC). Sources of low grade heat can include any process stream from which recovery of at least part of its heat content in the form of electricity is desired. These streams are often conventionally subjected to cooling with air and/or water, since they are not at a sufficiently high temperature for economically useful heat integration applications (e.g., preheating, low-, medium- or high-pressure steam generation, or distillation column reboiling). The temperature of these sources of low grade heat is generally from about 75° C. to about 180° C. and often from about 50° C. to about 120° C. Representative streams as sources of low grade heat include refining and petrochemical process streams having temperatures within these ranges, with particular examples being overhead vapors, and more generally overhead products, from vapor-liquid contacting apparatuses such as distillation columns and other columns (e.g., absorbers, strippers, quenching towers, scrubbers, etc.) as described above. Other good examples are product run-down coolers, for example the desorbent cooler within an aromatics complex, especially for pre-heater services. Other examples of low temperature heat sources are reactor effluent streams after process exchange prior to typical air cooled product condensers.

Distillation columns refer to those used in separation processes based on differences in the relative volatility of components present in an impure mixture. Distillation involves the purification of components having differing relative volatilities by achieving multiple theoretical stages of vapor-liquid equilibrium along the length of a vertical column. Rising vapor, enriched in a lower boiling component relative to the liquid from which it is vaporized in a lower stage in the column, is contacted with falling liquid, enriched in a higher boiling component relative to the vapor from which it is condensed in a higher stage in the column.

Distillation columns, which also include fractionation columns that provide number of product fractions, each having components within certain boiling point ranges, are widely used, for example, in separating effluents of reaction zones. Reaction zones generally comprise one or more reactors that are used to convert (e.g., catalytically) a feedstock to the more valuable reactor effluent, containing the product fractions that are subsequently resolved through fractionation. Hydrocarbon-containing feeds to vapor-liquid contacting apparatuses such as distillation columns therefore include reactor effluents or otherwise upgraded hydrocarbon products comprising at least a portion of a reactor effluent, optionally after initial treatments or separations (e.g., in single stage high-, medium-, and/or low-pressure separators to remove hydrogen and/or light hydrocarbons such as methane). These hydrocarbon-containing feeds generally comprise at least about 80% by weight, and often comprise at least about 90% by weight, hydrocarbons.

The claimed invention is a process for using waste heat to drive multiple compressor services within an aromatics complex. There are several sources of heat located near power consumers with the complex. There are two potential waste heat sources, where column overhead condensers and process coolers are located. The location above a toluene column may be used and the location above a para-xylene extraction zone may be used. However, it is contemplated that other locations may also be used. Recycle gas compressors may be located in locations outside the toluene extraction zone and in locations outside the isomerization zone. However, it is contemplated that other locations may also be used.

Methods for using waste heat to drive multiple compressor services within an aromatics complex, according to representative embodiments of the invention, are illustrated in the FIGURE. As shown, fractionation column 100 fractionates hydrocarbon feed 5, which may, for example, be an upgraded hydrocarbon product from the reaction zone of a petrochemical process. As discussed above, overhead product 10, which may be completely or substantially in the vapor phase, is generally removed from fractionation column 100 at a temperature that renders it a low grade heat source suitable for power generation according to methods described herein. Overhead product 10 may also be cooled somewhat, after exiting fractionation column 100, to a suitable temperature for this application. Overhead product 10 may be all or a portion of the net overhead withdrawn from fractionation column 100.

According to the embodiment shown in the FIGURE, overhead product 10 is passed to evaporator 200 for indirect heat exchange with organic fluid 18, generally having a boiling point that is from about 5° C. to about 14° C. lower than the temperature of an overhead product 10. All the operating pressure of the ORC system are adjustable to match the refrigerant properties with the heat source temperatures. Suitable organic fluids include fluorocarbons and chlorofluorocarbons (CFCs) that are used commercially as refrigerants. Representative fluorocarbons include 1,1,1,3,3-pentafluoropropane (HFC-245fa), 1,1,1,2-tetrafluoroethane (HFC-134a), 1,1,2,2-tetrafluoroethane (HFC-134), 1,1,1,3,3-pentafluorobutane (HFC-365mfc), 1,1,1,2,3,3,3-heptafluoropropane (HFC-227ea), and mixtures thereof. Representative CFCs include CFC-113 (1,1,2-trichloro-1,2,2-trifluoroethane), CFC-11 (trichlorofluoromethane), CFC-12 (dichlorodifluoromethane), CFC-22 (chlorodifluoromethane), and mixtures thereof. Mixtures of fluorocarbons and chlorofluorocarbons may also be used in an organic fluid.

Indirect heat exchange, in evaporator 200, between overhead product 10 and organic fluid 18, provides cooled overhead product 20, having a temperature that is generally from about 10° C. to about 75° C. less than that of overhead product 10 immediately prior to the heat exchange. In representative embodiments, cooled overhead product 20 has a temperature generally from about 50° C. to about 125° C., and often from about 65° C. to about 100° C., immediately after exchanging heat. Some or all of the heat removed from overhead product 20, as a result of indirect heat exchange, may be latent heat that causes condensation of at least a portion of cooled overhead product 20 (and an overall increased liquid fraction of this product), as opposed to sensible heat that causes a temperature decrease of this product.

Also, exiting evaporator 200, as a result of indirect heat exchange, is vapor-enriched fluid 22, having an increased vapor fraction relative to organic fluid 18. Preferably, vapor-enriched fluid 22 is completely in the vapor phase after exiting evaporator 200. Vapor-enriched fluid 22 is then utilized in turboexpander wheel(s) 300 to drive an electrical generator (for electricity generation) or other type of load. The turboexpander 300 is directly connected with a generator 320 and one or more compressors 340, 350. Power supplied by the refrigerant to the turboexpander is transferred directly to the compressor service(s) via an internal or external gear such as a bull gear with multiple pinions. The generator may be used as a motor for startup of the compressor services initially using power supplied from the power grid, and then convert to a generator supplying power to the grid as the ORC system operation commences to provide power from the low temperature heat recovery.

In an effort to consolidate an aromatics complex related compression equipment, using recycle gas stream 340 and recycle gas stream 350 from different units into a single installed turbomachinery asset. In one example, recycle gas stream 340 originates from a toluene unit and recycle gas stream 350 originates from an isomerization unit. It should be recognized installation of a single, multi-service compressor and turboexpander asset offers dramatic initial capital cost and installed cost advantages when compared against installing 3 separate, dedicated assets, for example the toluene unit recycle gas compressor 340, the isomerization unit recycle gas compressor 350 and the ORC turboexpander 300 and generator set 320.

The application of machine type described retains the ability to independently compress recycle gas streams without cross contamination of process streams (340/350/ORC refrigerant) or any compromise to critical process performance. As illustrated in the FIGURE, there is a process boundary 342 and a process boundary 344. It should be recognized the toluene unit and isomerization unit reactor loops have optimum performance at different operating pressures and temperatures. Opportunities exist to use inlet guide vanes to maximize operating flexibility for each service (340, 350, 300) while minimizing compressor power requirements at the lowest first cost.

To establish a complete ORC, turboexpander exhaust 24 from turboexpander 300 may be condensed, for example using air cooled exchanger 400, to regenerate organic fluid 18, which is generally completely in the liquid phase. The example shown in the FIGURE uses a wetted surface air cooler (WSAC) which is preferred to minimize the temperature of the refrigerant, minimize the size of the air cooler, and achieve optimum ORC energy. Organic fluid 18 may then be pumped via pump 500 for indirect heat exchange, as discussed above, in evaporator 200.

Often, cooling of overhead product 10 using evaporator 200 replaces at least part of the cooling using conventional air and/or water indirect heat exchangers to reject the low grade heat to the environment. Cooled overhead product 20 may, in some cases depending on its temperature, be further cooled, such as a water cooled exchanger or trim condenser, prior to passing to overhead receiver 700.

The exchangers 600 are used for refrigerant stream 18 pre-heating. In the example shown in the FIGURE, pre-heating is done using two exchangers 600. However, it is contemplated that in other embodiments, pre-heating may use additional process exchangers. The pre-heaters may be arranged in series or in parallel to match the available low temperature heat of the aromatics complex. In another embodiment, there may also be an exchanger between the turboexpander exhaust stream 24 and the condenser 400 that exchanges heat with pumped refrigerant before the evaporator service 200.

The condenser 400 having an advanced cooling technology proposed is a wet surface air cooler (WSAC). In this technology, water is sprayed on the tubes of the air cooler while air is induced downward over the tube bundles. Air is then disengaged from the water, and the water is recirculated. The water significantly improves the heat transfer coefficient, and vaporization transfers heat from the water to the air directly. The system design is more compact and modular relative to typical cooling water systems, as it minimizes the cooling tower, heat exchanger, pumps, and associated piping. Some key WSAC advantages include having the coldest possible outlet temperature, water conservation due to higher concentration of impurities allowed, compact footprint, lower parasitic energy vs. traditional water cooling, and competitive cost and maintenance.

These pre-heaters can be in series or in parallel to match the available low temperature heat of the aromatics complex. In overhead receiver 700, the vapor phase is removed as net column overhead 26 and the liquid phase is returned as reflux 28 back to fractionator 100.

Overall, aspects of the invention are directed to methods for generating electrical power from low grade heat sources from refining and petrochemical processes, including overhead products such as overhead vapors from vapor-liquid contacting apparatuses, including distillation columns, absorbers, strippers, quenching towers, scrubbers, etc. Rather than rejecting the low temperature heat contained in these vapors to cooling air and/or cooling water, the vapors may instead be used to evaporate an organic working fluid. The vapors of the working fluid may then be sent to a turboexpander to drive a generator or other load, thereby reducing overall utility requirements and emissions, such as CO₂, otherwise generated in electricity production.

In view of the present disclosure, it will be seen that several advantages may be achieved and other advantageous results may be obtained. Those having skill in the art will recognize the applicability of the methods disclosed herein to any of a number of refining, petrochemical, and other processes. Those having skill in the art, with the knowledge gained from the present disclosure, will recognize that various changes could be made in the above processes without departing from the scope of the present disclosure. Mechanisms used to explain theoretical or observed phenomena or results, shall be interpreted as illustrative only and not limiting in any way the scope of the appended claims.

While the invention has been described with what are presently considered the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but it is intended to cover various modifications and equivalent arrangements included within the scope of the appended claims.

SPECIFIC EMBODIMENTS

While the following is described in conjunction with specific embodiments, it will be understood that this description is intended to illustrate and not limit the scope of the preceding description and the appended claims.

A first embodiment of the invention is a process for using waste heat, comprising passing a column waste heat stream from a column to an expanding zone to produce a compressed stream wherein the expanding zone includes a turboexpander having a turboexpander wheel(s), one or more compressor service(s), and a generator in a single installed machine; passing the compressed stream to a condensing zone to produce a condensed stream; passing the condensed stream to a preheating zone to produce a preheated stream; passing the preheated stream to an evaporation zone to produce an evaporated stream; and passing the evaporated stream back to the column. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph, wherein the column waste heat stream may originate from multiple waste heat sources in the aromatics complex. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph, wherein the waste heat stream has a temperature of about 100° C. to about 140° C. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph, wherein the column may be any column within an aromatics complex. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph, wherein the column is an extract column. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph, wherein the column is a reformate splitter. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph, wherein the column is an A₈ stripper. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph, wherein the preheating section includes a plurality of preheaters. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph, wherein the evaporation zone includes a plurality of evaporators.

A second embodiment of the invention is an apparatus for using waste heat, comprising an inlet in direct communication with a column having an overhead line; the overhead line in direct communication with an evaporation zone having an overhead line in direct communication with a expanding zone and an outlet line in direct communication with an overhead receiver; the expanding zone having a expanding zone outlet line in direct communication with a condensing zone having a compressing zone outlet line wherein the expanding zone includes a turboexpander having a turboexpander wheel(s), one or more compressor service(s), and a generator in a single installed machine; the condensing zone outlet line in direct communication with preheating zone having a preheating zone outlet line; and the preheating zone outlet line in direct communication with the evaporation zone. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the second embodiment in this paragraph, wherein the waste heat stream is a vapor-enriched fluid. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the second embodiment in this paragraph, wherein the waste heat stream has a temperature of about 100° C. to about 140° C. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the second embodiment in this paragraph, wherein the column may be any column within an aromatics complex. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the second embodiment in this paragraph, wherein the column is an extract column. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the second embodiment in this paragraph, wherein the column is a reformate splitter. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the second embodiment in this paragraph, wherein the column is an A₈ stripper. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the second embodiment in this paragraph, wherein the preheating section includes a plurality of preheaters. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the second embodiment in this paragraph, wherein the evaporation zone includes a plurality of evaporators.

Without further elaboration, it is believed that using the preceding description that one skilled in the art can utilize the present invention to its fullest extent and easily ascertain the essential characteristics of this invention, without departing from the spirit and scope thereof, to make various changes and modifications of the invention and to adapt it to various usages and conditions. The preceding preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limiting the remainder of the disclosure in any way whatsoever, and that it is intended to cover various modifications and equivalent arrangements included within the scope of the appended claims.

In the foregoing, all temperatures are set forth in degrees Celsius and, all parts and percentages are by weight, unless otherwise indicated.

Claims

1. A process for using waste heat, comprising:

passing a column waste heat stream from a column to an expanding zone to produce a compressed stream wherein the expanding zone includes a turboexpander having a turboexpander wheel(s), one or more compressor service(s), and a generator in a single installed machine;

passing the compressed stream to a condensing zone to produce a condensed stream;

passing the condensed stream to a preheating zone to produce a preheated stream;

passing the preheated stream to an evaporation zone to produce an evaporated stream; and

passing the evaporated stream back to the column.

2. The process of claim 1, wherein the column waste heat stream may originate from multiple waste heat sources in the aromatics complex.

3. The process of claim 1, wherein the waste heat stream has a temperature of about 100° C. to about 140° C.

4. The process of claim 1, wherein the column may be any column within an aromatics complex.

5. The process of claim 1, wherein the column is an extract column.

6. The process of claim 1, wherein the column is a reformate splitter.

7. The process of claim 1, wherein the column is an A8 stripper.

8. The process of claim 1, wherein the preheating section includes a plurality of preheaters.

9. The process of claim 1, wherein the evaporation zone includes a plurality of evaporators.

10. An apparatus for using waste heat, comprising:

an inlet in direct communication with a column having an overhead line;

the overhead line in direct communication with an evaporation zone having an overhead line in direct communication with a expanding zone and an outlet line in direct communication with an overhead receiver;

the expanding zone having a expanding zone outlet line in direct communication with a condensing zone having a compressing zone outlet line wherein the expanding zone includes a turboexpander having a turboexpander wheel(s), one or more compressor service(s), and a generator in a single installed machine;

the condensing zone outlet line in direct communication with preheating zone having a preheating zone outlet line; and

the preheating zone outlet line in direct communication with the evaporation zone.

11. The apparatus of claim 10, wherein the waste heat stream is a vapor-enriched fluid.

12. The apparatus of claim 10, wherein the waste heat stream has a temperature of about 100° C. to about 140° C.

13. The apparatus of claim 10, wherein the column may be any column within an aromatics complex.

14. The apparatus of claim 10, wherein the column is an extract column.

15. The apparatus of claim 10, wherein the column is a reformate splitter.

16. The apparatus of claim 10, wherein the column is an A8 stripper.

17. The apparatus of claim 10, wherein the preheating section includes a plurality of preheaters.

18. The apparatus of claim 10, wherein the evaporation zone includes a plurality of evaporators.