US2679833A - Generation and superheating of vapor by burning combustible gas - Google Patents

Description

June l, 1954 2,679,833

L. V. ANDREWS ETAL GENERATION AND SUPERHEATING OF VAPOR BY BURNING COMBUSTIBLE GAS Filed Dec. l, 1948 /N VEN i'a/?5 V OL L/.SON CFA/G 5 L l/ NDREWJ ZBY Patented June 1, 1 954 GENERATION AND SUPERHEATING OF VAPOR BY BURNING COMBUSTIBLE GAS L. V. Andrews and Ollison Craig, Worcester, Mass., assignors to Riley Stoker Corporation, Worcester, Mass., a corporation of Massachusetts Application December 1, 1948, Serial No. 62,854

Claims.

This invention relates to the generation and superheating of vapor by burning combustible gas, and more particularly to an apparatus whereby the temperature of superheated vapor may be accurately controlled despite wide variations in the rate of vapor generation.

When steam is to be used for power purposes, it is the common practice to employ a steam boiler and an associated steam superheater, these parts being constructed and arranged to utilize the heat derived from the combustion of uel. In many such installations the superheater receives all or a very substantial part of its heat by convection from the combustion gases after they have left the furnace, the furnace itself usually having water cooled walls to absorb radiant heat. When a steam generating unit of this type is in operation, it is found that the temperature of the steam leaving the superheater will vary with changes in the steam output. This is undesirable, and many attempts have been made to maintain a substantially constant steam temperature, but the prior arrangements have been subject to various disadvantages. In some cases dampers are required to control the flow of hot gases, but it is dificult to provide dampers which will close tightly when necessary and which will withstand the severe Operating conditions. Injection of water into the steam is a known practice, but unless the water is distilled it will contaminate the steam. Desuperheaters of the indirect contact type are expensive and often require complicated piping.

It is accordingly one object of the invention to provide a comparatively simple, inexpensive, and dependable apparatus for generating and superheating vapor to a predetermined temperature by burning combustible gas.

It is a further object of the invention to provide a novel apparatus for controlling the temperature of superheated vapor, such as to avoid the disadvantages of the prior art.

With these and other objects in view, as will be apparent to those skilled in the art, the invention resides in the combination of parts set forth in the specification and covered by the claims appended hereto.

Referring to the drawings illustrating one embodiment of the invention, and in which like reference numerals indicate like parts,

Fig. 1 is a vertical section through a gas burner and a portion of an associated urnace wall; and

Fig. 2 is a vertical longitudinal section through a steam generating and superheating unit, with the burner of Fig. 1 mounted in operative position thereon.

nace or combustion chamber I 0 having a front wall ll, a rear wall l2, and two opposed side walls 14 (one only being shown). A horizontal water drum !5 is located adjacent the top of the rear wall !2, and a small horizontal water drum or header !6 is located adjacent the top of the front wall ii. A horizontal steam-and-water drum [8 is mounted above the rear water drum !5 and is connected thereto by a bank of upright water tubes lt. Two rows of water tubes extend upwardly from the front portion of the water drum !5 and then forwardly to the drum 16. A row of water tubes 22 leads upwardly and rearwardly from the drum I 6 to the drum !8 and serves to support a roof 23. A superheater 24 is mounted above the water tubes 20 and beneath the roof 23, the rear ends of the superheater tubes being connected to the drum !8 to receive steam therefrom, and their front ends being connected to a steam outlet header 25. A bafile 21 extends upwardly from the drum !5 behind the upright portions of the water tubes 20, and a baiile 28 extends downwardly from the drum !8 behind the two front rows of water tubes 19. A wall 30 is located behind the rearmost row of water tubes [9. A scot hopper 3! is provided between the bottom of the wall 30 and the water drum !5, and

a gas outlet duct 32 is provided at the top of the V wall 30, this duct having a damper 33 therein.

Rows of water wall tubes 35 and 36 are associated A with the front and rear walls ll and |2 respectively, and a row of water wall tubes 37 is associated with each of the side walls !4. As so far described the steam generating and superheating apparatus is of a Well-known Construction.

In order to obtain the heat necessary for operation of the apparatus, combustible gas and air are introduced into the urnace as two elements for combustion to mix with one -another, thereby producing a fiame and hot gaseous products of combustion. steam is generated in the various water tubes, particularly in the tubes which are in position to receive and absorb heat radiated by the fiame, and this lowers the temperature of the combuston gases. The steam travels through the superheater 24, which is in a position to receive heat from the hot gases mainly by convection.

For the purpose of controlling the temperature 4 of the superheated steam, we vary the luminosity of the fiame and thereby vary the rate at which heat is radiated therefrom to the surrounding water tubes. In this manner we are able to alter the temperature of the gases reaching the superheater and thus obtan control of the superheated steam temperature. In order to make possible the required variation in flame luminosity, we preferably direct portions of one of the combustion elements in two separate paths. One of these paths is such as to bring about a comparatively slow mixing of the elements and a luminous flame. The other path is such as to bring about a comparatively rapid mixing of the elements and a non-luminous fiame. The rflame luminosity is controlled by varying the relative rates of flow in the respective paths.

Referring now particularly to ig. 1, it will be seen that the front wall l l of the furna'ce is provided with an opening 40 for the admission of' the fuel and air. In front of this opening there is mounted a burner box 4! forming a plenum chamber to which air is supplied under pressure from a suitable source through a duct 42 equipped with the usual dampers 63. Air flows rearwardly from the box 41 through an opening 35 in the rear wall thereof and thence through the furnacewall opening 46. This air stream is preferably caused to spin about the axis of the opening 40; in known manner, by means of angularly positioned vanes or louvers 46 located within the box 41; A fuel nozzle sa is axially aligned with the furnace wall opening 40 in position to discharge a comparatively large jet of combustible gas rearwardlytherethrough. This gas will mix with the surrounding air rather slowly, producing a highly luminous flane within the iurnace. A conical bale 49 may be mounted on the rear end of the nozzle to deflect the air stream away from the fuel jet and thus still further delay the mixing. If desred, a few small openings 53 may be provided through this baffle. Between the burner box 4l and the wall H, and surrounding the wall opening 40, there is mounted a gas ring 52 in the'form of a, hollow torus having a series of orifices 53 from which comparatively small jets of combustible gas are directed inwardly toward the axis of the ring and at a slight angle rearwardly toward' the furnace. Since these gas jets travel inwardly across the air stream which flows through the opening w, the gas and air will mix very rapidly, producing a substantially nonluminous flame within the furnace.

By controlling the relative proportions of fuel gas delivered to the central nozzle 38 and to the ring 52 we are able to vary the luminosity of the fl'ame and there'by control the temperature of the superheated steam. Various forms of apparatus may be employed for this'purpose. In the particular embodinent illustrating there is provided a three-way valve 55 having a valve member 55 controlled by an Operating lever 51. This valve has an inlet 59 which is supplied with fuel gas by a pipe 50, an outlet 62 which is connected to the gas ring 52' by a pipe 83, and an outlet 65 which is connected to the central nozzle ta by a pipe 36. In order to provide automatic control for the valve 56' there is shown a' power relay 33 of a suitable and well-known type having an arm 69 connected to the valve lever 51 by a link TO. A temperature responsive bulb 12 is mounted within the superheater'outlet header 25 and connected to the relay 68. by a small tube ?3. This bulb may be of a known type containing a volatile liquid which will vary the fluid pressure at the relay 68 if any variation occurs in the steam temperature.

The operation of the invention will now be apparent from the above disclosure. A suitable combustible gas, such as naturalgas, will be de livered through the pipe 60 to the three-way valve 55 at a rate required by the current demand for steam. Some of this gas will flow through the pipe 63 to the gas ring 52 and be discharged from the orifices 53. The remainder of the gas will flow through the'pipe 68 and be discharged rom the nozzle 48. Air from the duet e?. will flow past the dampers 43 and the louvers i& to the opening l and thence through the wall opening ot, mixing with the gas to produce a flame and hot gaseous products of combustion in the furnace These hot gases will travel upwardly past the tubes 20 into contact with the superheater 24, downwardly behind the baflie 21, and upwardly behind the baffie 28 to the outlet duct 32. Steam will be generated in the various heat-exposed water tubes and released in the drum !8, whence it will travel through the superheater 24 to th header 25. If the temperature of the steam in this header increases above a desh-ed value, the bulb 'Z will increase the fluid pressure transmitted through the tube 13 to the relay 58, which will respond by lowering the arm 69 and the valve lever 51. This will turn the valve member 523 in a counter-clockwise direction to cause a greater proportion of the fuel gas to flow through the central nozzle 13, thereby increasing the luminosity of the flame. This will increase the radiation of heat from the flame to the water tubes surrounding the furnace and thus reduce th temperature of the hot gases `reaching the superheater, so that less heat will be transmitted by convection to the steam and its temperature will be loWered. Similarly, if the stean temperature drops appreciably below the desired value, the bulb ?2 will decrease thefluid pressure transmitted through the tub 13 to the relay 58. consequently the relay arm 69 will move upwardly, lifting the valve lever 51 and turning the valve member 53 in a clociwise direction. This will increase the proportion of the fuei gas flowing through the gas ring 52, and decrease the luminosity of the name. Hence less heat will be radiated from the flame to the surrounding water tubes, the temperature of the hot gases reaching the superheater will be increased, more heat will be transmitted by convection to the steam, and the temperature of the steam will b raised. In this manner, the steam. temperature may be accurately controlled.

It will be recognized that the invention provides a highly advantageous apparatus for controlling the temperature of superheated vapor in vapor generators fired by gas. the apparatus is comparatively simple and inexpensive. If desired, the relay 3 ma; be omitted, and th valve lever may then be controlled manually. Any movement of this lever, whether produced automatically or manually, will efiect a very pronpt adjustment of the vapor temperature.

Having thus described our invention, what we claim as new and desire to secure by Letters Patent is:

1. Apparatus for generating and superheating vapor comprising walls 'forming a furnace, a burner to introduce a combustible gas and air as two elements of combustion into the iurrace to produce-a flame and gaseous products of combuston, the burner providing two separate conduits O' portions of one of said elements, one Conduit being such that the portion of the element discharged therefrom will mix rather slowly with the other element to produce a comparatively luminous fiame andthe other conduit being such that the portion of the element discharged therefrom will mix rather rapidly with the other element to produce a comparatively non-luminous flame, means to control the relative rates of flow in the two conduits and the resultant fiame luminosity, vapor generating elements in position to absorb heat radiated by the flame, and a vapor superheater in position out of the presence of the vapor generating elements to receive heat mainly by convection from the said gaseous products.

2. Apparatus for generating and superheating vapor comprising walls forming a furnace, a burner to introduce a combustible gas and air into the furnace to produce a fiame and gaseous products of combustion, the burner providing two separate conduits for portions of the gas, one conduit being such that the portion of the gas discharged therefrom will mix rather slowly with the air to produce a comparatively luminous flame and the other conduit being such that the portion of the gas discharged therefrom will mix rather rapidly with the air to produce a comparatively non-luminous ame, means to control the relative rates of gas flow in the two conduits and the resultant flame luminosity, vapor generating elements in position to absorb heat radiated by the fiame, and a vapor superheater in position out of the presence of the superheater to receive heat mainly by convection from the said gaseous products.

3. Apparatus as set forth in claim 2, in which a three-way valve is provided to control the relative rates of gas fiow in the said two conduits.

4. Apparatus as set forth in claim 3, in which means is provided to control the three-way valve e automatically in response to variations in the temperature of the vapor leaving the superheater to cause more gas to flow through the said one Conduit when it is desired to lower the superheat.

5'. Apparatus for generating and superheating vapor comprisng walls forming a furnace, a burner to introduce combustible gas and air into the furnace to produce a flame and gaseous products of combustion, the burner including a nozzle arranged to discharge a large jet of gas free from air and a hollow gas ring surrounding said nozzle having a series of orifices arranged to. discharge small jets of gas free from air transversely of the gas from said nozzle into an air stream flowing through the gas ring, means to direct gas in controlled relative proportions to the central nozzle and to the gas ring, vapor generating elements in position to absorb heat radiated by the flame, and a vapor superheater in position out of the presence of the vapor generating elements to receive heat mainly b'y convection from the said gaseous products.,

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,338.902 Brown May 4, 1920 2,098,659 Harper Nov. 9, 1937 2,100,190 Jackson Nov. 23, 1937 2,229,643 De Baufre Jan. 28, 1941 2,367,193 Blizard Jan. 16, 1945 2,575,885 Mittendorf Nov. 20, 1951

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