AU2010361358B2

AU2010361358B2 - Waste heat boiler

Info

Publication number: AU2010361358B2
Application number: AU2010361358A
Authority: AU
Inventors: Hans Georg Christiansen
Original assignee: Haldor Topsoe AS
Current assignee: Topsoe AS
Priority date: 2010-09-30
Filing date: 2010-09-30
Publication date: 2014-05-08
Anticipated expiration: 2030-09-30
Also published as: UA108669C2; AU2010361358A1; DK2622297T3; ZA201301534B; JP2013539006A; KR20140005865A; EP2622297A1; BR112013006139A2; WO2012041344A1; PL2622297T3; EP2622297B1; US20130180475A1; CN103270383A; MX2013003048A; ES2541838T3; EA201390473A1; JP5746353B2; CA2811676A1; CN103270383B

Abstract

A waste heat boiler has heat exchange tubes for indirect heat exchange of a relatively hot process gas and a cooling media, and a by-pass tube for by-passing a part of the process gas; a process gas collector collects and mixes a part of the heat exchanged process gas and at least a part of the by-passed process gas before the mix is lead via a control valve to the process gas outlet of the waste heat boiler together with the rest of the heat exchanged process gas.

Description

WO 2012/041344 PCT/EP2010/005968 Title:Waste Heat Boiler Background of the invention The present invention is directed to the recovery of waste 5 heat from chemical reactions. More particularly, the inven tion relates to a waste heat boiler with improved control of cooling effect. Waste heat boilers are most generally used for the gen eration of steam by waste heat recovered from hot process 10 streams. Typically, those boilers are designed as shell-and tube exchangers with a plurality of heat exchanging tubes ar ranged within a cylindrical shell. Two basic types of shell-and-tube exchangers are em ployed in the industry, the water-tube type, in which wa 15 ter/steam mixtures flow through the tubes, and the fire-tube type having the heating process stream inside the tubes. The characteristic components of the boiler are the tubes mounted in tubesheets at a front-end head and a rear end head within the shell. In the fire-tube boilers steam 20 production is accomplished on the shell side of the tubes by indirect heat exchange of a hot process stream flowing through the boiler tubes. The shell side is through a number of risers and down-comers connected to a steam drum, which may be arranged above or as an integral part of the boiler 25 shell. The mechanical design and, in particular, dimensioning of the heat exchanging surface in shell-and-tube exchanger type boilers represent certain problems. Fire-tube boiler ap plications involve high pressures on the shell side or on 30 both sides, and considerable temperature differences between the shell side and the tube side. Particular considerations CONFIRMATION COPY WO 2012/041344 PCT/EP2010/005968 2 have to be given to fouling and corrosion characteristics of the process stream. Boilers handling fouling and/or corrosive process streams must be designed to a higher duty than required when 5 clean in order to allow for satisfying lifetime under serious fouling and/or corroding conditions. The heat transferring surface of the boiler tubes has further to be adapted to ex pected corrosion and fouling factors in the stream. To pro vide for a desired and substantially constant cooling effect 10 during long term operation of the boilers, appropriate heat transfer and temperature control is required. Conventionally designed boilers are equipped with a by pass of a relative large diameter tube (relative to the heat exchange tube diameter), which may be internal or external to 15 the boiler shell. The by-pass is usually constructed as an insulated tube provided with a flow control valve. During initial operation of the boilers, part of the hot process stream is by-passed the heat transferring tubes to limit the heat transfer within the required level. 20 After a certain time, on stream fouling and/or corrosion of the tubes increase, leading to decreased heat transfer. The amount of by-passed process stream is then reduced, which allows for higher flow of the process stream through the heat transferring tubes to maintain the required cooling effect. 25 A major drawback of the known boilers of the above type is vigorous corrosion on the metallic surface of the by-pass, particularly the by-pass outlet and flow control valve, which are in contact with the un-cooled process stream at tempera tures as high as 1000 0 C or even higher. Known art has sought 30 to solve this problem in various manners such as cooling the control valve with a cooling fluid or to avoid a hot by-pass stream and in stead divide the heat exchanger in different 3 sections with different heat-exchange level and therefore different process gas outlet temperatures. Examples of known art are disclosed in US5452686A, US2007125317A, US4993367A, GB1303092A, US1918966A and EP0357907A. 5 Summary of the invention It would be desirable to avoid the drawbacks of the known waste heat boilers by providing a boiler of the shell-and tube heat exchanger type with an improved heat transfer and 10 temperature control. It would also be desirable to provide a waste heat boiler with a simpler and less expensive design than known art waste heat boilers. It would be further desirable to provide a waste heat 15 boiler with a process gas by-pass tube and a control valve for simple control of the by-pass process gas stream and accordingly the process gas outlet temperature, without exposing the control valve to excessive temperatures leading to corrosion. 20 In one aspect there is provided a waste heat boiler for heat exchanging a relatively hot process gas with a cooling media comprising a a shell part, 25 e at least two tube sheets, * a plurality of heat exchange tubes, * at least one by-pass tube, * a heat exchange section enclosed by said shell part and said at least two tube sheets 30 a a process gas inlet section, e a process gas outlet section, * at least one cooling media inlet, 3a e at least one cooling media outlet,the relatively hot process gas enters the heat exchange tubes and the at least one by-pass tube in the process gas inlet 5 section, flows through the heat exchange section where at least the process gas flowing in the heat exchange tubes is in indirect heat exchange with the cooling media and exits in the process gas outlet section, wherein said waste heat boiler further comprises a 10 control valve and an outlet process gas collector, said control valve is enabled to control the volume stream of the process gas which flows through said outlet process gas collector, the process gas collector collects at least a part of the process gas exiting the 15 at least one by-pass tube and the cooled process gas exiting a part of the heat exchange tubes. According to one embodiment of the present invention there is provided a waste heat boiler for heat exchanging a 20 relatively hot process gas with a cooling media where the waste heat boiler comprises at least one shell part (a heat exchange section second shell part), and at least two tube sheets placed in an inlet end and an outlet end of the heat exchange section second shell part, whereby this second 25 shell part and the two tube sheets enclose the heat exchange section of the waste heat boiler. A plurality of heat exchange tubes and at least one process gas by-bass tube are placed in the heat exchange section and are fixed in the first tube sheet near the first end of each tube and fixed 30 in the second WO 2012/041344 PCT/EP2010/005968 4 tube sheet near the second end of each tube. At least one cooling media inlet and at least one cooling media outlet are located on the waste heat boiler to enable a cooling media to flow into and out of the heat exchange section on the shell 5 side of the tubes. The cooling media is thus enclosed by the second shell part and the first and the second tube sheet. A process gas inlet section is located near the first tube sheet, on the opposite side than the cooling media. The inlet section may further be enclosed by a first shell part at the 10 process gas inlet end. A process gas outlet section is lo cated near the second tube sheet also on the opposite side of the cooling media. Also the outlet section may further be en closed by a third shell part. In the third shell part in the process gas outlet end, an outlet process gas collector is 15 located such that it collects at least a part of the process gas exiting the at least one by-pass tube and also collects the cooled process gas exiting a part of the heat exchange tubes. 20 Process gas flows from the first shell part, process gas inlet end, to the heat exchange tube inlets and the by-pass tube inlet, through the heat exchange tubes and the at least one by-pass tube, out of the heat exchange tube outlets and the at least one by-pass process gas outlet to the third 25 shell part, process gas outlet end. A cooling media flows into the heat exchange section via the cooling media inlet and is in contact with the shell side of the heat exchange tubes and can be in contact with the shell side of at least one by-pass tube before the cooling media exits the heat ex 30 change section through the cooling media outlet. The process gas enters the process gas inlet section at a first tempera ture and exits the heat exchange tubes at a second relatively WO 2012/041344 PCT/EP2010/005968 5 low temperature. The process gas exiting the by-pass tube has a third temperature which is lower or equal to the first tem perature, but higher than the second temperature. The outlet process gas collector mixes at least a part of the by-pass 5 process gas and a part of the heat exchanged process gas. Thus, the mixed process gas temperature has a fourth tempera ture which is higher than the second temperature, but lower than the third temperature. The amount of heat exchanged process gas and the amount of by-pass gas in this mix is com 10 posed such that this fourth temperature is low enough to pre vent excessive corrosion of the control valve which is lo cated downstream of the collected by-pass and heat-exchanged process gas. The control valve controls the amount of mixed process gas in the total process gas stream exiting the waste 15 heat boiler. The total process gas stream exiting the waste heat boiler should be of a certain fifth temperature, which is higher than or equal to the second temperature, but lower than the fourth temperature. The control valve can control the volume flow of mixed process gas as compared to the total 20 exiting process gas volume flow and thus control the fifth temperature even with varying second and fourth temperatures and volume flows. Accordingly, with a constant high first temperature and the aim of a constant low fifth temperature, but a rising second temperature due to fouling/corrosion of 25 the heat-exchange pipes; the fifth temperature can be kept constant by use of the control valve to decrease the volume flow of the by-pass process gas having a fourth temperature. According to a further embodiment of the invention, the mix 30 ing of the heat exchanged process gas and the by-passed proc ess gas in the outlet process gas collector can be enhanced by mixing means located in the collector up-stream of the WO 2012/041344 PCT/EP2010/005968 6 control valve. The mixing means can be of any known function and materials. In a further embodiment of the invention, there is one by 5 pass tube and the collector collects the process gas exiting the one by-bass tube and the heat-exchanged process gas exit ing at least one of the heat exchange tubes. In another embodiment of the invention, the process gas inlet 10 section is lined with a ceramic liner for protecting the first shell part from the relative hot process gas. In a further embodiment of the invention also the by-pass tube, the mixing means and the process gas collector can be 15 lined with a ceramic liner. In an embodiment of the invention, the cooling media can be water or it can be steam. The cooling media can be water when entering the heat exchange section and a part of the water or 20 all of the water can be heated by the indirect heat-exchange with the relative hot process gas such that all or a part of the cooling media exiting the heat exchange section via the cooling media outlet is steam. 25 In a further embodiment of the invention, the second shell part or both the first, the second and the third shell part can be substantially cylindrical. The cylindrical shape can be advantageous as it is a pressure robust and material sav ing shape. By substantial is meant any shape which is oblong 30 in one cross sectional view and any shape.which is not far from circular in another cross sectional view, such as circu lar, elliptic, square, pentagonal, hexagonal etc.

WO 2012/041344 PCT/EP2010/005968 7 In a further embodiment of the invention, a plurality of heat exchange tubes are placed in a substantially circular array in the tube sheets and the by-pass tube or the at least one 5 by-pass tube is placed substantially in the center of the ar ray. By substantially is meant, that the location does not have to be mathematically accurate, the shapes can vary to a large extent as long as consideration to heat-exchange effec tiveness and material costs are respected. 10 In an embodiment of the invention, the waste heat boiler is used in a process plant producing wet sulphuric acid. Features of the invention 15 1. Waste heat boiler for heat exchanging a relatively hot process gas with a cooling media comprising * a shell part, e at least two tube sheets, 20 e a plurality of heat exchange tubes, e at least one by-pass tube, e a heat exchange section enclosed by said shell part and said at least two tube sheets * a process gas inlet section, 25 e a process gas outlet section, e at least one cooling media inlet, e at least one cooling media outlet, the relatively hot process gas enters the heat exchange tubes and the at least one by-pass tube in the process gas inlet 30 section, flows through the heat exchange section where at least the process gas flowing in the heat exchange tubes is WO 2012/041344 PCT/EP2010/005968 8 in indirect heat exchange with the cooling media and exits in the process gas outlet section, wherein said waste heat boiler further comprises a control valve and an outlet proc ess gas collector, said control valve is enabled to control 5 the volume stream of the process gas which flows through said outlet process gas collector, the process gas collector col lects at least a part of the process gas exiting the at least one by-pass tube and the cooled process gas exiting a part of the heat exchange tubes. 10 2. Waste heat boiler according to feature 1, wherein the outlet process gas collector further comprises mixing means located up-stream of the control valve, for mixing the rela tively hot process gas exiting the at least one by-pass tube 15 with the cooled process gas exiting a part of the heat ex change tubes. 3. Waste heat boiler according to any of the preceding fea tures comprising one by-pass tube, wherein the outlet process 20 gas collector collects the process gas exiting the bypass tube gas and the exiting process gas of at least one of the heat exchange tubes. 4. Waste heat boiler according to any of the preceding fea 25 tures, wherein the process gas inlet section is lined with a ceramic liner. 5. Waste heat boiler according to feature 4, wherein fur ther the inside wall of the bypass tube is lined and at least 30 part of the outlet process gas collector is lined with a ce ramic liner.

WO 2012/041344 PCT/EP2010/005968 9 6. Waste heat boiler according to any of the preceding fea tures, wherein the cooling media is water or steam or both water and steam. 5 7. Waste heat boiler according to any of the preceding fea tures, wherein said shell has a substantially cylindrical shape and said at least two tube sheets have a substantially circular shape. 10 8. Waste heat boiler according to any of the preceding fea tures, wherein said heat exchange tubes are arranged in a circular array in the tube sheets and said by-pass tube is arranged substantially in the centre of said array. 15 9. Process for heat exchanging a relatively hot process gas with a cooling media in a waste heat boiler according to any of the preceding features comprising the steps of, * providing the relative hot process gas to the process gas inlet section, 20 * providing the cooling media to the heat exchange section of the waste heat boiler * heat-exchanging a first part of the relatively hot proc ess gas with the cooling media indirectly in the heat exchange tubes located in said heat exchange section 25 e by-passing a second part of the relatively hot process gas from the process gas inlet section, through the heat exchange section and to the process gas outlet section without substantial heat exchange with the cooling media e collecting and mixing at least a part of the by-passed 30 process gas and a part of the cooled process gas in an outlet process gas collector WO 2012/041344 PCT/EP2010/005968 10 controlling the volume stream of the collected and mixed process gas with a control valve. 10. Use of a waste heat boiler according to any of the fea 5 tures 1-8 in a process plant producing Sulphuric Acid. Position Number Overview. 100 Waste Heat Boiler, WHB 10 110 First shell part, process gas inlet end 111 Lining 112 Process gas inlet section 113 By-pass process gas inlet 114 Heat exchange tube inlet 15 115 First tube sheet, process gas inlet end 120 Second shell part, heat exchange section 121 Cooling media inlet 122 Cooling media outlet 123 Heat exchange tube 20 124 Process gas by-pass tube 125 Second tube sheet, process gas outlet end 126 Heat exchange section 130 Third shell part, process gas outlet end 132 Process gas outlet section 25 133 By-pass process gas outlet 134 Heat exchange tube outlet 135 Control valve, by-pass tube outlet 136 Outlet process gas collector 137 Outlet process gas mixing means 30 138 mixed process gas outlet WO 2012/041344 PCT/EP2010/005968 11 Fig. 1 is a cross sectional view of the waste heat boiler 100 according to an embodiment of the invention. The waste heat boiler comprises a first shell part, process gas inlet end 110; a second shell part, heat exchange section 120 and a 5 third shell part, process gas outlet end 130; all having a substantially cylindrical shape and substantially the same diameter, but as can be seen on the figure, not necessarily the same material thickness. The material thickness as well as the choice of material can be varied depending on the 10 process conditions. A first tube sheet, process gas inlet end 115 separates the first shell part from the second shell part. Likewise, a sec ond tube sheet, process gas outlet end 125 separates the sec 15 ond shell part from the third shell part. Thus the first shell part and the first tube sheet encloses the process gas inlet section 112; the second shell part along with the first and the second tube sheet encloses the heat exchange section 126; and the third shell part and the second tube sheet en 20 closes the process gas outlet section 132. The internal sur face of the process gas inlet section can have a liner 111, for instance a ceramic liner to protect the internal surfaces from the high temperatures of the inlet process gas. 25 The first and the second tube sheets have corresponding bores to accommodate heat exchange tubes 123. The heat exchange tubes stretch at least from the first tube sheet through the heat exchange section and at least to the second tube sheet. The connection between each heat exchange tube and each of 30 the tube sheets are made gas and liquid tight. Each heat ex change tube has a heat exchange tube inlet 114 located in the WO 2012/041344 PCT/EP2010/005968 12 process gas inlet section and a heat exchange tube outlet 134 located in the process gas outlet section. The first and the second tube sheets also have at least one 5 corresponding bore for at least one process gas by-pass tube 124. In the embodiment of the invention according to fig. 1 there is one process gas by-pass tube. The connection between the process gas by-pass tube and the first and the second tube sheet is made gas and liquid tight. The process gas by 10 pass tube has a by-pass process gas inlet 113 located in the process gas inlet section and a by-pass process gas outlet 133 located in the process gas outlet. The process gas by pass tube can be provided with a lining (not shown) which can protect the tube from the relative high process gas tempera 15 tures and which may also reduce the indirect heat exchange between the cooling media and the by-passed process gas. In the heat exchange section a cooling media inlet 121 pro vides fluid connection of a cooling media to the heat ex 20 change section. The at least one cooling media inlet can be located in any position on the second shell part or even on the first or the second tube sheet, as long as fluid connec tion to the heat exchange section is provided. A location on the shell part of the heat exchange section is shown on fig. 25 1. A cooling media outlet 122 located in fluid connection to the heat exchange section provides outlet of the cooling me dia from the heat exchange section. Each of the heat exchange tubes and the process gas by-pass 30 tube thus provides fluid connection from the process gas inlet section through the heat exchange section and to the process gas outlet section, thereby enabling the process gas WO 2012/041344 PCT/EP2010/005968 13 to flow through the heat exchange section without direct con tact to the cooling media. The process gas flowing in the heat exchange tubes is in indirect heat-exchange with the cooling media, whereas the part of the process gas which is 5 by-passed, i.e. flowing in the process gas by-pass tube is in less or relative low or substantially no indirect heat exchange with the cooling media: If the by-pass tube is not lined, the by-passed process gas will have some heat-exchange with the cooling media, but the heat-exchange in the by-pass 10 tube will be relative lower than the heat-exchange in the heat exchange tubes due to the by-pass tube's higher volume to surface ratio. If the by-pass tube is lined, for instance with a ceramic liner, the indirect heat-exchange between the by-passed process gas flowing in the by-pass tube and the 15 cooling media will be relative low or close to zero. In any case, the temperature of the heat-exchanged process gas exit ing the heat exchange tube outlets is considerably lower than the temperature of the by-passed process gas exiting the by pass process gas outlet. 20 In the process gas outlet section, an outlet process gas col lector 136 is located. It collects the by-passed process gas and a part of the heat-exchanged process gas. In the embodi ment according to fig. 1, the process gas collector collects 25 the by-passed process gas and the heat-exchanged process gas exiting the heat-exchange tubes located nearest to the by pass tube in a circular array around the by-pass tube. Outlet process gas mixing means are located inside the process gas collector ensuring mixing of the by-passed and the part of 30 the heat-exchanged process gas to an extent so the control valve, by-pass tube outlet 135 is not exposed to a critical 14 amount of process gas with a temperature so high it will lead to substantial corrosion of the control valve. Said control valve controls the amount of mixed process gas 5 which is exited from the outlet process gas collector to the process gas outlet section. Thus, as the temperature of the heat-exchanged process gas is lower than the temperature of the mixture of the by-passed and the heat-exchanged process gas exiting the mixed process gas outlet 138, the control 10 valve can vary the temperature of the process gas exiting the process gas outlet section within an interval between the temperature of the heat-exchanged gas and the mixed by pass gas. Or more important, the control valve can keep the temperature of the process gas exiting the process gas 15 outlet section on a certain level, even though the temperature of the heat-exchanged process gas vary due to for instance reduced indirect heat-exchange because of for instance fouling in the heat-exchange tubes. 20 Fig. 2 shows the waste heat boiler of fig. 1 with the temperatures noted. The temperatures have the following relations: ti a t 3 > t 4 > t 2 t4 > Ts a t 2 25 Comprises/comprising and grammatical variations thereof when used in this specification are to be taken to specify the presence of stated features, integers, steps or components or groups thereof, but do not preclude the presence or 30 addition of one or more other features, integers, steps, components or groups thereof.

Claims

1. Waste heat boiler for heat exchanging a relatively hot process gas with a cooling media comprising * a shell part, e at least two tube sheets, e a plurality of heat exchange tubes, * at least one by-pass tube, " a heat exchange section enclosed by said shell part and said at least two tube sheets * a process gas inlet section, " a process gas outlet section, e at least one cooling media inlet, " at least one cooling media outlet, the relatively hot process gas enters the heat exchange tubes and the at least one by-pass tube in the process gas inlet section, flows through the heat exchange section where at least the process gas flowing in the heat exchange tubes is in indirect heat exchange with the cooling media and exits in the process gas outlet section, wherein said waste heat boiler further comprises a control valve and an outlet process gas collector, said control valve is enabled to control the volume stream of the process gas which flows through said outlet process gas collector, the process gas collector collects at least a part of the process gas exiting the at least one by-pass tube and the cooled process gas exiting a part of the heat exchange tubes.

2. Waste heat boiler according to claim 1, wherein the outlet process gas collector further comprises mixing means located up-stream of the control valve, for mixing the relatively hot process gas exiting the at least one by-pass 16 tube with the cooled process gas exiting a part of the heat exchange tubes.

3. Waste heat boiler according to any one of the preceding claims comprising one by-pass tube, wherein the outlet process gas collector collects the process gas exiting the bypass tube gas and the exiting process gas of at least one of the heat exchange tubes.

4. Waste heat boiler according to any one of the preceding claims, wherein the process gas inlet section is lined with a ceramic liner.

5. Waste heat boiler according to claim 4, wherein further the inside wall of the bypass tube is lined and at least part of the outlet process gas collector is lined with a ceramic liner.

6. Waste heat boiler according to any one of the preceding claims, wherein the cooling media is water or steam or both water and steam.

7. Waste heat boiler according to any one of the preceding claims, wherein said shell has a substantially cylindrical shape and said at least two tube sheets have a substantially circular shape.

8. Waste heat boiler according to any one of the preceding claims, wherein said heat exchange tubes are arranged in a circular array in the tube sheets and said by-pass tube is arranged substantially in the centre of said array. 17

9. Process for heat exchanging a relatively hot process gas with a cooling media in a waste heat boiler according to any one of the preceding claims comprising the steps of, e providing the relative hot process gas to the process gas inlet section, * providing the cooling media to the heat exchange section of the waste heat boiler * heat-exchanging a first part of the relatively hot process gas with the cooling media indirectly in the heat exchange tubes located in said heat exchange section " by-passing a second part of the relatively hot process gas from the process gas inlet section, through the heat exchange section and to the process gas outlet section without substantial heat exchange with the cooling media * collecting and mixing at least a part of the by-passed process gas and a part of the cooled process gas in an outlet process gas collector * controlling the volume stream of the collected and mixed process gas with a control valve.

10. Use of a waste heat boiler according to any one of the claims 1-8 in a process plant producing Sulphuric Acid.

11. Waste heat boiler for heat exchanging a relatively hot process gas with a cooling media substantially as hereinbefore described with reference to either one of the Figure drawings. HALDOR TOPSOE A/S WATERMARK PATENT & TRADE MARK ATTORNEYS P3714SAUOO