Systems and Methods for Heat Recovery Steam Generation at Dual Pressures

Abstract

Systems for the recovery of heat from hot air exhaust from industrial processes, and the utilization of recovered heat to generate steam at two discrete (high and low) pressures. The systems match steam production with demand. The systems utilize efficient finned tube exchange units made up of modular sections that can be selectively associated with either high or low pressure steam generators. The systems utilize separate steam domes for each of the discrete steam pressures. The steam dome components may be structured apart from the heat exchange components. Each steam dome utilizes its own sensor and control instrumentation to vary the allocation of heat recovered to either or both the high or low pressure steam generator. The two generator subsystems are linked to operate variably according to demand. Monitoring upstream heat and downstream steam requirements allow for automated operation and allocation of recovered heat into the two subsystems.

Description

CROSS REFERENCES TO RELATED APPLICATIONS

This application claims the benefit under Title 35 United States Code §119(e) of U.S. Provisional Application 61/613,403 filed Mar. 20, 2012, the full disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to systems for the recovery of heat from industrial processes and the generation of steam there from. The present invention relates more specifically to a system for recovering heat from an industrial process and generating steam at both high and low pressures with the recovered heat.

2. Description of the Related Art

Many industrial processes utilize both high pressure and low pressure steam to carry out the manufacturing or industrial process. Such industrial processes generally also generate and release heat into the atmosphere as part of the operation of the industrial system. It is often desirable to recapture energy in the form of heat from such hot air streams that might otherwise be lost into the atmosphere. The present invention not only captures such otherwise lost energy from industrial hot air streams, but also generates steam that can be utilized within the industrial processes in a manner that recycles a portion of the energy and reduces the need for ancillary energy to operate the process. As part of this efficiency, the present invention is structured to permit the generation of steam from the recovered heat at both high pressure and low pressure, thereby providing dual pressure steam back to the industrial process rather than a single pressure steam flow.

One objective of the present invention is to produce both high pressure and low pressure steam from the same unit. The advantage of such a device over systems previously employed is that it makes it easier to match the steam production with the steam demand within the plant or manufacturing facility. If only high pressure steam is generated from a heat recovery system, then there would still be a considerable amount of heat left in the hot air stream that would continue to be lost to the atmosphere. This is because the exit air temperature of the hot air stream can not be lower than the temperature of the steam being produced. On the other hand, if only low pressure steam is generated, it is often the case that too much steam is generated for the demand and a considerable amount of energy must again be released into the atmosphere.

SUMMARY OF THE INVENTION

The present invention provides systems and methods for the recovery of heat from hot air exhaust streams produced by a wide variety of industrial processes, and the utilization of that recovered heat to generate steam at two discrete (high and low) pressures. By adjusting and balancing the use of the recovered heat to produce more or less high pressure steam and low pressure steam, the system of the present invention is able to match steam production with the demand for steam within the plant or manufacturing facility. The system utilizes a highly efficient finned tube exchange unit made up of multiple modular sections that can be selectively associated with either the high pressure steam generator or the low pressure steam generator. In conjunction with the array of modular exchange sections, the present invention utilizes a separate steam dome for each of the discrete steam pressures generated. The steam dome (two in the preferred embodiment) components may be structured and supported apart from the heat exchange components in order to reduce the overall weight of the basic unit. Each steam dome utilizes its own instrumentation and ancillary flow equipment (level controls, pressure switches, safety valves, etc.) in order to vary the allocation of heat recovered to either or both of the high pressure steam generator or the low pressure steam generator. The two discrete steam generator systems are linked so as to be capable of operating variably according to demand. To facilitate this, the modular heat exchanger sections each have their own inlet and outlet tubings built into the frame of each section. These heat exchanger sections may then be selectively directed to either the high pressure steam dome or the low pressure steam dome. Monitoring of the upstream heat being released and the downstream steam requirements allow for manual or automated operation and allocation of the recovered heat into the two sub-systems within the steam generator unit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A & 1B are schematic flow diagrams of the overall system of the present invention divided across two pages for clarity.

FIG. 2 is a perspective view of a first preferred embodiment of the present invention showing the heat exchange components and the dual steam dome components.

FIG. 3 is a front elevational view of the first preferred embodiment of the present invention shown and described above in conjunction with FIG. 2.

FIG. 4 is a top plan view of the first preferred embodiment of the present invention shown and described above in connection with FIG. 2.

FIG. 5 is a side elevational view of the first preferred embodiment of the present invention shown and described above in connection with FIG. 2.

FIG. 6 is a schematic block diagram showing the typical quantitative functioning of the system of the present invention, providing representative quantities of high pressure and low pressure steam generated with a given hot air flowthrough.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference is made first to FIGS. 1A & 1B which show in a schematic flow diagram the overall system of the present invention divided across two pages for clarity. FIGS. 1A & 1B disclose not only the liquid and gas flow lines, but also the hot air exhaust flow through the system. In addition, an array of sensors and electronic control devices are shown incorporated into the system for carrying out the automated operation of the system based upon levels, temperatures, and pressures within the system. An actual unit constructed according to the system and method described herein may appear as in the structural configuration shown in FIGS. 2-5. The schematic diagram of FIGS. 1A & 1B represents just such a structural system, albeit omitting certain ancillary components that would be optional and apparent to those skilled in the art of steam generators and heat exchange systems. The fundamental features of the present invention are disclosed and described in detail in the schematic of FIGS. 1A & 1B.

FIG. 1A discloses most of the external flow lines that connect into or out from the system of the present invention, as well as one-half of the heat exchange component of the system (the half associated with the low pressure steam generator side of the system). FIG. 1B represents the high pressure steam side of the heat recovery steam generating (HRSG) system associated with the first half of the heat exchange component. As indicated above, various electrical and electronic signal connections are made throughout the system to various sensors in the form of pressure gauges, level sensors, temperature sensors, and flow meters. Additionally, a number of remotely operated (electronic signal line) valves, pumps, and pressure release devices are shown to be operable in conjunction with automated control systems for such steam generator environments within plants and manufacturing facilities.

Reference is next made to FIG. 2 for a structural view of an example of a first preferred embodiment of the present invention shown implemented in conjunction with a heat exchange steam generator system of modest scale and complexity. In FIG. 2, heat recovery steam generator (HRSG) system 10 is made up primarily of heat exchange unit 12 and two steam dome/steam generator components 14 & 16. In the view shown in FIG. 2, steam dome 14 provides the high pressure steam generation, while steam dome 16 provides the low pressure steam generation. Hot exhaust air flows through heat exchange unit 12 through a bank of finned tube exchange sections that make up a single heat exchange unit 12. The number of heat exchange sections 20 that make up unit 12 may increase or decrease depending upon the demands of the system and the industrial process that the unit is associated with Flow from the steam domes into the heat exchange unit is carried out through the array of flow lines 26 (30 for high pressure steam dome) and the return from the heat exchange unit to the steam domes is carried out by way of return lines 24 (14 for high pressure steam dome) and return lines 22 (16 for low pressure steam dome). Each steam generator sub-system, made up primarily of steam domes 14 & 16, carries its own operational control and instrumentation assembly 28, typically comprising the necessary control valves, level sensors, pressure sensors, and other elements required for monitoring and controlling the operation of the overall system.

Reference is next made to FIG. 3 which is a front elevational view of the system shown generally in FIG. 2. In this view, system 10 again is shown to comprise heat exchange unit 12 as well as high pressure steam dome 14 and low pressure steam dome 16. In this view, the flow of hot exhaust air through the system occurs from the right hand side at air flow 36 and exits to the left hand side of this view at air flow 38. Operational monitoring and control once again occurs at control assembly 28 for high pressure steam generator sub-system and at control assembly 32 for low pressure steam generator sub-system. Flow lines 26 from high pressure steam dome 14 are shown directed into heat exchange sections 34 as described above. In a similar manner, low pressure steam dome 16 is connected by flow lines 30 to heat exchange sections 20 on the left hand side of the system. In this manner, the hottest exhaust air enters the system on the high pressure steam generator side and exits the system on the low pressure steam generator side.

FIG. 4 discloses in additional detail a top plan view of the overall system 10 described above, again showing the manner in which the exhaust gas flows through the system.

FIG. 5 shows an elevational view of the side of the system, describing in greater detail the array of sensor and control components associated with each of the steam dome/steam generator sub-systems.

Reference is finally made to FIG. 6 which provides a schematic block diagram showing the typical quantitative functioning of the system of the present invention. This schematic presents the production of representative quantities of high pressure and low pressure steam. FIG. 6 provides as an example, the operation of the system of the present invention at an altitude of 200 m (for atmospheric pressure purposes) with a total energy recovered at 3153 kW. In this example, exhaust air inlet temperature is a representative 360° C. with a flow of 1400 cubic meters per minute. Various density and humidity parameters to the exhaust flow are likewise provided in the figure. A heat transfer totaling 1804 kW occurs in the high pressure heat recovery steam generation stage of the process. This generates steam at a pressure of 17 barg at a temperature of 207° C. Source condensate is provided to the high pressure side of the system at 0.3 barg and a condensate temperature of 107° C. The exhaust air temperature after the high pressure steam stage of the system is a typical 235° C.

The low pressure steam generation stage of the system accomplishes a heat transfer of 1350 kW and produces steam at a pressure of 1 barg and a temperature of 120° C. The exhaust air outlet from the low pressure HRSG may be a typical 140° C. Source condensate is again provided to the low pressure HRSG at pressure 0.3 barg and a condensate temperature of 107° C.

Consideration of the heat recovered as shown in FIG. 6 indicates that the system provides a highly efficient mechanism for recovering energy otherwise lost from an industrial process and recycling it into the production of both high pressure and low pressure steam. The ability to balance and allocate the steam production in this manner between the dual pressures allows for a greater amount of energy to be recovered and re-utilized in the industrial process.

Although the present invention has been described in conjunction with a number of preferred embodiments, those skilled in the art will recognize modifications to these embodiments that still fall within the scope of the invention. Variations in the temperature and flow rate of the exhaust air inlet into the system may require corresponding variations in both the size and geometry of the heat exchange sections that make up the heat exchange unit. The modular construction of the heat exchange unit in the present invention lends itself to easy modification of the size and of the allocation of the heat exchange sections to the overall system and to the separate high pressure steam and the low pressure steam generating stages of the system. Various levels of automated operation of the system are also anticipated. A given industrial process that does not itself vary in its heat output may require little modification of an established balance between the generation of high pressure steam and low pressure steam.

Other industrial processes may require an ongoing monitoring and balance of the system based upon exhaust air temperatures and flows, as well as process steam requirements (high pressure or low pressure). The system of the present invention provides a versatile and easily modifiable system for recovering heat from an exhaust air flow in an industrial process and directing and utilizing that heat to efficiently generate steam in a balanced allocation of high pressure steam and low pressure steam.

Claims

1. A steam generation system for recovering heat from industrial process hot air exhaust streams and generating steam at two discrete pressures, the system thereby defining a high pressure steam generation subsystem and a low pressure steam generation subsystem, the overall steam generation system comprising:

a finned tube heat exchange unit positioned in association with the hot air exhaust streams, the heat exchange unit comprising a plurality of modular sections, the plurality of modular sections selectively associated with either the high pressure steam generation subsystem or the low pressure steam generation subsystem; and

first and second steam domes operable in conjunction with the plurality of modular sections of the heat exchange unit, the first and second steam domes discretely associated with the two steam generation subsystems, the steam domes structured and supported apart from the heat exchange unit.

2. The system of claim 1 wherein each steam dome further comprises separate control instrumentation and ancillary flow equipment.

3. The system of claim 2 wherein the ancillary flow equipment comprises level controls, pressure switches, and safety valves, the ancillary flow equipment provided to vary the allocation of heat recovered to the generation of either or both high pressure steam or low pressure steam.

4. The system of claim 1 wherein the high and low pressure steam generation subsystems are operationally linked to operate variably according to demand.

5. The system of claim 4 wherein each of the plurality of modular heat exchanger sections comprise discrete inlet and outlet connections, whereby the heat exchanger sections may be selectively directed to either the high pressure steam dome or the low pressure steam dome.

6. The system of claim 1 further comprising an upstream heat monitor for measuring a quantity of upstream heat being released and a downstream steam requirement monitor for measuring a quantity of high pressure steam required and a quantity of low pressure steam required.

7. The system of claim 6 further comprising automated control instrumentation for allocation of the recovered heat into the two subsystems within the steam generator unit.