MXPA99004417A - On-line regenerative air preheater fouling sensing system - Google Patents

Abstract

A fouling sensing system (42) monitors fouling of a rotary regenerative preheater (10) having a housing (12) and a rotor (14) rotatably mounted therein. An emitter (48) for emitting energy is positioned at one of the faces of the rotor (14) and emits energy through the rotor (14). A sensor (54) is positioned at the other face of the rotor (14) for receiving the energy and generating an output signal indicative of the intensity of the energy.

Description

SYSTEM FOR DETECTION OF INCRUSTATIONS IN ONLINE REGENERATIVE AIR PREHEATERS BACKGROUND OF THE INVENTION The present invention relates to the field of rotary regenerative pre-heaters for use in systems for the generation of energy by combustion. More specifically, this invention relates in general to a detection system for a rotary regenerative preheater. Rotary regenerative pre-heaters are well known for transferring heat from a post-combustion flue gas stream to a pre-combustion air stream. Conventional rotary regenerative air preheaters have a circular housing and a rotor rotatably mounted there. The rotor contains heat transfer elements for the transfer of heat from the flue gas stream to the air stream. The housing defines a flue gas inlet duct, a flue gas outlet duct, an air inlet duct and an air outlet duct. Sector plates divide the pre-heater into one side of air and one side of flue gas, where the hot flue gas accesses the flue gas inlet and passes through the rotor. The hot flue gas transfers heat to the thermal transfer elements in the rotor. The cold flue gas leaves the preheater through the flue gas outlet. A stream of air passes the heater through an air inlet and passes through the heated rotor. The thermal transfer elements of the rotor transfer heat to the air stream and the heated air leaves the pre-heater through the air outlet duct. Soot and other particles in the flue gas stream can be deposited in the heat transfer elements of the rotor. These deposits are typically collected at the hot end of the thermal transfer surface of the rotor. In addition, fly ash in the flue gas can be combined with moisture and sulfur derivatives to form a scale or deposit of fine grains, particularly at the cold end of the thermal transfer surface of the rotor. The collection of deposits at the hot and cold ends of the rotor affect the flue gases and air flow and degrade thermal transfer performance. Conventionally, the thermal transfer elements of the rotor have been cleaned using soot washing and blowing equipment. The soot blowing equipment uses steam over heated or dry compressed air to remove soot and other particles from the heat transfer elements. When soot blowing is inadequate to remove deposits, the rotor wash starts. Washing equipment requires that the rotary regenerative preheater be removed from the line in order to perform the cleaning procedures. The conventional washing equipment uses water to dissolve soot and other particles from the heat transfer elements. The frequency required for soot blowing of the rotor is typically determined by verification of the pressure drop across the rotor. However, the pressure drop verification has proven to be an unreliable indicator of soot accumulation. Typically, a pressure drop large enough to alert the operator indicates that deposits of scale have already accumulated to a point where they are difficult to remove. Therefore, the soot blowing must have started at a previous moment. This is particularly true of temperature-shifted fouling such as ammonium bisulfate formulation that typically occurs in a range of 30.48 to 60.96 cm (12 to 24") within the total element depth typically ranging from 187.96 to 304.8 cm (74 to 120"). This narrow band of scale deposits will not increase the pressure drop across the total depth of the element to a detectable degree until it has drastically reduced the open flow area in the embedded band. In this point, the penetration of soot blowing is greatly reduced by the restriction of that band and therefore the deposit can not be easily removed. As a result of the deficiencies in pressure drop verification, soot blowing typically starts at a synchronized frequency. The synchronized frequency soot blowing typically shortens the life of the element, since a very conservative soot blowing schedule with high frequency is often used. The synchronized frequency soot blowing can also be shown to be inadequate when a disturbance occurs in the operation of the boiler, embedding the rotor of the pre-heater between programmed soot blowing cycles. SUMMARY OF THE INVENTION Briefly stated, the invention in the preferred form is a system for detecting incrustations in regenerative air preheater, in line, for measuring the accumulation of scale in the rotor of a rotary regenerative preheater. The preferred scale detection system of the invention has a emitter structure and a detector structure. The emitting structure for energy is placed in one of the ducts on either the air side or the flue gas side of the rotary regenerative heater. Placed in the opposite duct of the current where the emitter is located, there is the detector structure for the energy of the emitter. The structure of the emitter can emit an electromagnetic wave, sound or radiation of nuclear particles. The omitted energy passes through the rotor and is received by the detector structure. For a constant level of transmitted energy, the open passages through the thermal transfer element will allow some percentage of the transmitted energy to pass. The verification of the change or reduction in the energy received by the detector structure indicates the level of incrustations experienced by the thermal transfer elements. Therefore, soot blowing can be initiated only when required. The use of the indent detection system of the invention avoids unnecessary soot blowing and increases the useful life of the thermal transfer element by initiating soot blowing before the deposits are difficult to remove. An object of the invention is to provide an in-line regenerative air pre-heater scale detection system for detecting the amount of scale of the heat transfer elements in the preheater rotor. Another object of the invention is to provide a system for detecting scale, to allow a more efficient synchronization of soot blowing operations. An additional objective of the invention is to provide an inlay detection system for measuring the relative scale of thermal transfer elements. These and other objects of the invention will be apparent from a review of the specification and drawings. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a partial exploded view of a rotary regenerative preheater; Figure 2 is a cross-sectional view of a portion of the rotary regenerative preheater shown in combination with an scale detection system of the invention; Figure 3 is a sectional view of a portion of a rotary regenerative preheater shown in combination with a further embodiment of the scale detection system of the invention. DESCRIPTION OF THE PREFERRED MODALITY A rotary regenerative pre-heater is generally designated by the number 10. The preheater 10 has a cover 12 defining an internal cover volume 13. Rotationally mounted within the cover 12 is a rotor 14 having elements of conventional heat exchange for heat transfer. (See Figure 2). The rotor 14 has a rotor or arrow post 18 to support the rotor 14 for rotation within the cover 12. The rotor post 18 extends through a central hot end section 20 and a cold end central section 22. Connected to the cover 12 is a chimney gas inlet duct 24 and a chimney gas outlet duct 26 for the flow of flue gas heated through the preheater 10. Also connected to the cover 12 is an air inlet duct 28 and an air outlet duct 30 for the pre-combustion air flow through the preheater 10. The cover 12, the flue gas ducts 24, 26, and the air ducts 28, 30 form a preheating housing 15. Extending through the housing 15, adjacent the upper and lower faces of the rotor 14, are sector plates 32, 34 that divide the pre-heater 10 into an air side 36 and a side to the stack gas 38. arrows of Figure 1, indicates the air direction and flue gas flow through the preheater 10. Hot flue gas entering through the flue gas inlet duct 24, transfers heat to the heat transfer elements in the continuously rotating rotor 14. The elements Heat transfer sensors are then rotated to the air side 36 of the rotary regenerative pre-heater 10. The heat stored from the heat transfer elements is then transferred to the combustion air stream which enters through the air inlet duct 28 The chilled flue gas exits the preheater 10 through the chimney flue gas outlet 26 and the heated pre-combustion air exits the preheater 10 through the air outlet duct 30. Soot, particulates, and compounds Chemicals in the flue gas stream are collected and condensed in the thermal transfer elements of the rotor 14 to form deposits and scale that restrict the flow of air and flue gas from the preheater 10. A soot blown apparatus 40 is typically placed in one of the ducts 24, 26, 28, 30 to remove these deposits of soot and scale from the heat transfer elements of the rotor 14. The soot blowing apparatus 40 is preferably placed in the chimney gas duct 26 to prevent fly ash from being blown into the wind boxes located downstream of the air side 36 of the preheater 10. The blowing apparatus of soot 40 blows steam on heated or dry compressed air on the thermal transfer elements of the rotor 14 to remove scale and deposits. A system for detecting scale in regenerative air pre-heaters, in line 42, according to the invention is placed to detect scale of the thermal transfer elements in the rotor 14. (See Figure 2). Accurate soot blowing timing for increased efficiency and rotor life can be achieved by using the scale detection system 42. The scale detection system 42 has an emitter structure 44 in a detector structure 46 along with instrumentation appropriate The scale detection system 42 is placed on either the air side 36 or the side for the flue gas 38 of the air pre-heater 10. The emitter structure 44 can be placed in any of the four ducts, the chimney gas inlet duct 24, the chimney gas outlet duct 26, an air inlet duct 28 or the air outlet duct 30. The detector structure 46 is placed on the other side of the elements of heat transfer from emitter structure 44, on the same side for air 36 or side for flue gas 38 of preheater 10. Scale detection system 42, preferably located on air side 36 of the preheater 10 in order to reduce the accumulation of soot, particles and other contaminants in the scale detection system 42. The emitter structure 44 has a source of emitter 48 supported in the air outlet duct by a support bracket 50. The Energy emitted by the emitting source 48 can be oriented electromagnetic waves such as lasers, or normal light having a more diffuse pattern. Electromagnetic waves can cover visible and non-visible frequencies. The source of emitter 48 can also emit sound, including frequencies in the range of ultrasonic and infrasound or emit nuclear particles or nuclear electromagnetic radiation (X-rays). The emitting source can be supplied by a transmitter cable 52 that passes through the housing 15 to a remote site (not shown). Nuclear sources have the advantage of not requiring an external energy source in order to function.

In addition, selection of a radioactive source with a prolonged half-life, or extended average life, allows a uniform output with reduced maintenance.

Although only one emitting source 48 has been illustrated, there may be a plurality of emitting sources mounted in multiple positions across the radius of the rotor to more effectively verify the entire rotor. Alternatively, a single emitting source can be mounted to move in and out through the radius. The detector structure 46 has a detector 54, mounted on a second support bracket 50. The appropriate detector 54 correlates with the selection of emitting source 48. The detector 54 is connected by a detector wire 56 which passes through the housing 15 to a unit for detector control and instrumentation (not shown). The detector 54 is preferably positioned generally opposite the emitting source 48. If the emitting source is mounted for movement, the detector 54 will also be mounted for synchronous movement. The transmitting source 48 preferably emits a constant level of transmitted energy. The open passages through the thermal transfer elements will pass or allow some percentage of the transmitted energy. The detector structure 46 verifies the change or reduction in the energy received after the energy passes through the rotor 14. The amount of scale can be correlated and the plant operator be warned that a soot blow cycle is required to start upon verification the reduction in energy over a period of operation. Most forms of electromagnetic emitting sources 48 will require a visual range through the thermal transfer elements of the rotor 14. Sources based on sound or based on high nuclear energy 48, will not require a direct visual range through the rotor thermal transfer elements 14. In an alternate embodiment of the invention, an indent detector system 142 has a emitter structure 144 and a detector structure 146. (See Figure 3). The detector structure 146 can also be placed either on the side of the chimney gas 38 or air side 36 of the preheater 10. The emitter structure 144 has a source emitter 148 located outside the housing 15. The source emitter 148 is preferably a source of light. The light from the emitting source 148 is directed through a gate 149 in the housing 15 and reflected from a reflector or mirror 151, preferably located in the air outlet duct 28. The mirror 151 is mounted in the duct air outlet 28 by a support bracket 50. The mirror 151 reflects the light from the emitting source 48 through the thermal transfer elements of the rotor 14. The detector structure 146 has a reflector or mirror 147, to reflect light from the emitting source 148 through a gate 145 in the housing 15. The detector structure 146 further has a detector 154 for receiving light from the emitting source 148 and generating an output signal indicative of the intensity of the received light. The output signal from the detector 154 is transferred to a central control system (not shown) on a detector wire 156. Alternatively, the emitting source 148 and the detector 154 can be located in the housing 15 within the ducts 24, 26, 28, 30. In a further embodiment of the detector structure 146, the reflectors or mirrors 147, 151 can be fiber optic cable.The light from the emitting source 148 can be trapped or focused on the fiber optic cable and transmitted to the detector 154, located in an accessible position outside the housing 15. Similarly, the light output of the emitting source 148 can be directed by an optical fiber cable through the housing 15 and directed through the thermal transfer elements. in the rotor 14 for detection by the detector structure 146. While preferred embodiments of the present invention have been illustrated and described in detail, it will be readily appreciated that many modifications Ions and changes are within the skill of those with ordinary skill in the specialty. Therefore, the appended claims are intended to cover any and all modifications that fall within the spirit and actual scope of the invention.

Claims (14)

REI INDICATIONS

1. - A system for detecting scale, to verify incrustations of a rotary regenerative preheater, the detection system is characterized in that it comprises: a preheater housing; a rotor rotatably mounted in the housing, the rotor defines opposed rotor faces; transmitting means for energy through the rotor, detecting means for detecting the energy of the emitting means sent through the rotor.

2. - The scale detection system according to claim 1, characterized in that the emitting means comprise an electromagnetic source.

3. - The scale detection system according to claim 1, characterized in that the pre-heater housing defines an air side and a flue gas side and the emitting means and the detector means are located on the Preheater housing air.

4. - The scale detection system according to claim 1, characterized in that the emitting means are placed on one of the faces of the rotor and the detector means are placed on the other side of the rotor faces.

5. - A system for detecting scale in a rotary regenerative pre-heater, the system for detecting scale is characterized in that it comprises: an enclosure that defines a side of flue gas and an air side, the air side comprises a duct air inlet and an opposite air outlet duct; a rotor rotatably mounted on the cover for rotation between the air inlet duct and the air outlet duct; emitting means placed in one of the air inlet duct and the air outlet duct to emit energy through the rotor, detector means placed in the other of the outlet duct and the inlet duct to detect the emitted energy of the emitting means .

6. - The scale detection system according to claim 5, characterized in that the emitting means comprise an electromagnetic source and the detector means comprise an electromagnetic detector.

7. - The scale detection system according to claim 5, characterized in that the emitting means comprise an acoustic source and the detector means comprise a sound detector.

8. - The scale detection system according to claim 5, characterized in that the emitting means comprise a source of nuclear radiation, the detector means comprising a nuclear radiation detector.

9. - A system for detecting scale in a rotary regenerative preheater, the system for detecting scale is characterized because it comprises: a preheater housing, the housing has one side for flue gas and one side for air, the side of air comprises an air inlet duct and an air outlet duct placed in the opposite manner; a rotor rotatably mounted in the housing for rotation between the air inlet duct and the air outlet duct; emitting means for sending electromagnetic energy within one of the air inlet duct and the air outlet duct; reflector means in the duct for the electromagnetic energy through the rotor, and sensor means for the energy transmitted through the rotor.

10. - The scale detection system according to claim 9, characterized in that the reflector means comprise a fiber optic cable.

11. The scale detection system according to claim 9, characterized in that the detector means comprises a second reflector means in the other of the air inlet duct and the air outlet duct and a detector outside the housing, the second reflector means are adapted to reflect the electromagnetic energy outside the housing to the detector.

12. - The scale detection system according to claim 11, characterized in that the second reflector means comprise a fiber optic cable.

13. - The scale detection system according to claim 11, characterized in that the second reflector means comprise a mirror.

14. - The scale detection system according to claim 9, characterized in that the reflector means comprise a mirror.