Abstract:
A waste heat recovery system comprising ducting to which hot gas is communicated, means to supply lower temperature diluent gas to the ducting, to mix with the hot gas, and produce a reduced temperature mixed gas stream, a vaporizer in communication with the ducting, to receive the stream and to transfer heat from the stream to a working fluid in the vaporizer to vaporize said fluid, and a blower operating to displace the stream through the vaporizer.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates generally to a low cost system to utilize waste heat produced in a process. 
     Recovery of waste heat from combustion sources is an important way to achieve energy conservation that is widely practiced in industry. The waste heat can be used to provide useful heat to a process or to generate power using a heat engine. Some examples are regenerative heating in a glass furnace, generation of hot water for heating from an engine exhaust and generation of steam for power generation from the exhaust of a large gas turbine. However, some sources of waste heat have characteristics that result in excessively high costs to generate useful thermal or power output. These include low temperature, small size, remote location and/or corrosive products. Some examples include landfill gas flares and engine generators which are remote from any useful thermal loads. 
     Accordingly, there is need for a low cost, efficient method to recovery the waste heat from sources which have not been widely used because of the heretofore uneconomic characteristics. 
     SUMMARY OF THE INVENTION 
     It is a major object of the invention to provide apparatus and methods meeting the above need. Basically, the apparatus of the invention includes a waste heat recovery system comprising: 
     a) ducting to which hot gas is communicated, 
     b) means to supply lower temperature diluent gas to the ducting, to mix with the hot gas, and produce a reduced temperature mixed gas stream, 
     c) a vaporizer in communication with the ducting, to receive the gas stream and to transfer heat from the stream to a working fluid in the vaporizer to vaporize that fluid, 
     d) and a blower operating to displace the gas stream through the vaporizer. 
     Typically, the blower is of induction type, having an inlet to which the mixed gas stream is supplied after passage through the vaporizer, i.e. the system operates by suction induced stream flow through the vaporizer, such suction also being utilized to induce mixing of the hot gas and cooler gas, in the ducting upstream of the vaporizer. A highly efficient system is thereby achieved. 
     Another object of the invention is to provide a through opening or openings in a side wall of the hot gas ducting, to pass the lower temperature diluent gas into the ducting in response to suction creation by the blower and communicated to said ducting via the vaporizer. A refractory sleeve or sleeves may be provided in the side wall opening or openings, to block loss of heat to the exterior of the ducting via the side opening or openings. 
     The system enables use of vaporized working fluid by means to create electric power; and a diverter valve may be advantageously supplied in series with the ducting to 
     i) divert said stream to atmosphere when the the above reference electric power producing means is not operating to produce electric power; 
     ii) pass said stream to the vaporizer when said means is operating to produce electric power. 
    
    
     These and other objects and advantages of the invention, as well as the details of an illustrative embodiment, will be more fully understood from the following specification an drawings, in which: 
     DRAWING DESCRIPTION 
     FIGS. 1-3 and  4  are system diagrams; 
     FIG. 3 a  is a top plan view taken on lines  3   a - 3   a  of FIG. 3; 
     FIG. 4 a  is a top plan view taken on lines  4   a - 4   a  of FIG.  4 . 
    
    
     DETAILED DESCRIPTION 
     Indirect Waste Heat Recovery System 
     An indirect waste heat removal system is illustrated in FIG. 1. A heat exchanger  1 , with the example having finned tubes, is installed in a hot gas source  3 . Air is passed through the heat exchanger by a blower  2 . A second blower  2   a , can be provided so that if the first blower fails, uninterrupted heat removal and heat exchanger cooling can be provided. 
     The heated air flows through ducting  1   a , to a diverter valve  4 . For times when power is being generated or heat is being used, the diverter valve is positioned so that the hot air is ducted at  4   a  to the thermal load. During times when the power system or thermal load is not operating, the diverter valve ducts at  4   b  the heated air to atmosphere, enabling the heat exchanger structure temperature to remain at its operating value. 
     For the generation of power, a vaporizer or boiler  6 , is provided. The hot air passes through the vaporizer, transferring heat to a working fluid such as water, hydrocarbons or refrigerants, and discharging at  6   a . The working fluid vaporizes. The vapor is ducted at  8 , through a control valve  9 , to a turbine  10 . The turbine shaft  10   a  drives a generator  11 , generating electrical power. The power is conducted through cables  11   a , to electric switchgear and protective relays  12 . The power can be conducted through another cable  12   a , to the utility grid  13 , or directly to an electrical load  13   a.    
     The vapor leaving the turbine at  10   b  flows to heat transfer tubing  15   b  in a condenser  15 , where heat is transferred to the atmosphere at  15   c , causing the vapor to condense to liquid. The liquid leaving the condenser at  15   a , is pressurized by a pump  16 , and returned through piping  7 , to the vaporizer tubing. Controls for the elements are shown at  17 . 
     Direct Waste heat Recovery System 
     A direct waste heat recovery system is shown in FIG. 2. A source  18  of hot gas is shown with insulated ducting  80 . Holes  21  in the ducting are provided with refractory or high temperature metal sleeves  20  to pass the hot gas. A manifold structure  19  is provided into which cooling air is sucked through manifold well holes  21 , which mixes with the hot gases to provide an outlet gas stream  22 , at the desired temperature. The outlet gas stream is pulled i.e. sucker through the vaporizer  23 , or another heat exchanger, by a blower  24 . The outlet gas stream leaving the blower at  24   a  has been cooled by the heat exchanged. The cooled outlet gas stream is exhausted at  25 , to atmosphere. Other elements the same as those in FIG. 1 bear the same numerals. 
     Another direct waste heat recovery system is shown in FIG. 3 that uses pipes with holes to suction the hot gas from the hot gas source  23 . A metal header pipe  30 , is attached  31 , to the hot gas duct  80 . Pipes  27  with holes  28  facing the hot gas stream are inserted endwise into the metal header pipe  30 . Caps  29 , are placed over projecting the ends of the pipes. The fit of the pipes  27  into the metal header pipe, and the fit of the caps  29  on the pipes can be a slip fit, enabling thermal expansion of the pipes to occur and enabling the pipes to be constructed of a material different from the metal header pipe, such as refractory or Inconel alloy. In the case of a vertical hot gas duct, the pipes can seat or rest on top  31   a  of the duct  80 , or be inserted through holes in the ducting, once again having a slip fit. The outlet gas stream at  31   b  is pulled through the vaporizer  31   c  or another heat exchanger, by the blower  31   d , and exhausted to atmosphere at  31   e . Blower  31   d  has its suction intake side connected to vaporizer chamber  90 . Other elements, the same as in FIG. 1, bear the same numerals. 
     Another direct waste heat recovery system with temperature control at  91  is shown in FIGS. 4 and 4 a . An inlet metal header  33  is attached  33   a , to the hot gas duct wall  32 . Another metal header pipe  37  is attached  37   a , to the opposite side of the hot gas duct. Pipes  37   b , with holes  37   c , facing the hot gas flow are inserted to project endwise into the metal header pipes to pass hot gas into the pipes. Holes  34  and  34   a  are provided in the headers to provide slip fit with the suction pipes  37   b , enabling easy assembly, thermal expansion, and the use of dissimilar materials. A control valve  35 , is provided on the open end of the metal header pipe  33  to regulate the amount of inlet air pulled into the metal inlet header pipe to mix with the hot exhaust gas received in pipes  37   b . A temperature sensor and transmitter  36 , is installed in the outlet metal header pipe  37  to measure the temperature of the outlet gas, as seen at  36   a . The output from the temperature sensor and transmitter is utilized to control the position of the control valve  35  such that the temperature of the outlet gas stream  38  is regulated at the desired temperature. The outlet diluent gas stream is pulled through the vaporizer  39 , or another heat exchanger, by the blower  40 , and exhausted to the atmosphere  41 . 
     Advantages 
     The advantages of the invention are: 
     1. An inexpensive method is provided to recover useful heat from a waste heat stream and generate power. 
     2. The indirect waste heat recovery system enables the use of lower temperature materials in the heat exchanger by providing two full capacity blowers and a diverter valve. 
     3. The direct heat recovery systems eliminate the use of a conventional heat exchanger which is more costly and heavy. 
     4. The use of an induction blower with slip fits for the suction pipes or sleeves reduces the fabrication cost and improves reliability. This design also enables the hot gas source to continue operating with no effect on the waste heat recovery system when the waste heat recovery system is not operating by turning off the blower. 
     5. The use of diluent air to reduce the temperature of the exhaust gas enables the use of less costly materials. 
     6. For vertical ducts, such as gas combustion (heat source) flares, the use of a structure that is supported by the outside surfaces and rests on top of the duct eliminates penetrations in the ducting. 
     7. The use of a temperature controlled valve for the air inlet is an inexpensive method to control the temperature of the outlet gas stream.