DE19926402C1 - Generating steam from gases produced by non-catalytic cracking of hydrocarbons comprises passing them through one tube of double-walled heat exchanger in water-filled container, with different fluid being passed through other tube - Google Patents

Abstract

Generating steam with hot process gases comprises using the gases to produce saturated steam. The gases are divided into several streams, each of which is passed through one tube (13a,14a,15a) of a double-walled heat exchanger (12) in a container filled with water. A different fluid is passed in counter-current through the other tube (13b,14b,15b). Generating steam with hot process gases, especially those produced by non-catalytic cracking of hydrocarbons by partial oxidation under increased pressure and at high temperature, comprises using the gases to produce saturated steam. The gases are divided into several streams, each of which is passed through one tube (13a,14a,15a) of a double-walled heat exchanger (12) in a container filled with water. A different fluid is passed in counter-current through the other tube (13b,14b,15b). An Independent claim is included for a steam generator for carrying out the above process.

Description

The invention relates to a method for generating steam by means of hot Process gases, in particular by means of the non-catalytic splitting of Hydrocarbons based on partial oxidation at high pressures and high temperatures generated process gases, in which the Process gases for the generation of saturated steam in a large number of individual flows by means of pipes through a standing container filled with water and are withdrawn in single streams from this and from the container Saturated steam is discharged.

From DE-OS 19 59 228 or the DE prospectus from L. & C. Steinmüller GmbH "Plant and apparatus construction components and circuits" (1986), p. 18, such a method is known, in which the method of a Process reactors brought in process gases in single streams by spiral coiled tubes downstream of the reactor as a waste heat boiler Heat exchanger are performed. There are several spirally wound tubes summarized to spiral heating surfaces by a flow jacket under Formation of a candle-like assembly are surrounded. The pipes are individually led out of the container and connected with collectors. The merged gas streams are possibly in after a further cooling fed to a separate tube bundle heat exchanger for gas scrubbing. Out saturated steam is drawn off from the container at the upper end. This saturated steam one is not explained as the total current High pressure hot steam generation (overheating by means of a fired Superheater) supplied.  

As hydrocarbons such. B. gases and oil or oil residues (Residuals) used. In the case of natural gas gasification, that is Pollution of the pipes carrying the gases is relatively low. However, at a pulsating burner operation in the reactor or when admixing Residual chemicals in the gas, at least temporarily, cause higher pollution, that so-called fouling occur.

In the gasification of petroleum from crude oil to the so-called residuals with increasing hydrogen sulfide and Heavy metal contents result in higher soot levels in the process gas lead to a higher tendency to contamination.

In the known procedure, there is a gas outlet side Individual isolation of the individual pipe strings of the container is proposed been made under operating conditions for cleaning purposes Increase in flow velocity in the unblocked pipes of the container is advantageous. The known process failed the use of an unfired superheater in the process gas stream so far that there is a concept for the gas-side cleaning of the Superheater heating surfaces / controllability of the superheated steam temperature was missing.

In the case of using a tube bundle heat exchanger with a large number of single pipes connected in parallel on the gas side for one on the process gas side the feed water preheater downstream of the waste heat boiler (evaporator) due to the missing individual shut-off on the shell and tube heat exchanger the entire consisting of waste heat boiler and feed water preheater Unit for cleaning the individual gas paths in the feed water preheater be taken out of operation. In addition, this concept is Risk of erosion due to the relatively high flow velocities in the Full load case, to master the partial load cases, considerably higher.

It is therefore the object of the invention to specify a method in which simple way during steam generation and using the Residual heat from the process gases emerging from the waste heat boiler the advantages an individual shut-off of individual process gas lines can be reached.  

This object is achieved in that the withdrawn from the container Process gas individual flows each on a tube of a double tube heat exchanger be guided, the other pipe with a different fluid flow is applied, and that at least one tube of the Double tube heat exchanger can be shut off on the gas outlet side.

In this procedure, a gas outlet side can be easily Barrier at the end of the gas outlet to use the residual heat Double tube heat exchanger done without everyone else Process gas individual flows must be shut down operationally. By the barrier becomes the flow rate in the neighboring Single flows in the waste heat boiler and in the double tube heat exchanger increased and the pipes carrying the individual flows are both in the waste heat boiler also in the double tube heat exchanger due to the speed increase of Deposits cleaned.

The barrier can be a purely individual barrier; however, it is also conceivably a small number of double tube heat exchangers merge on the gas outlet side and the barrier after Merge. This procedure also provides in Another one compared to switching off an entire tube bundle heat exchanger Single barrier.

Double tube heat exchangers are known per se (see VDI Heat Atlas 1953 - Approximate heat transfer figures for some types of heat exchangers Bl. C b 5). They preferably consist of at least two coaxial ones Double pipe sections, the inner pipe sections over a - if necessary. detachable - connecting bend and its external pipe sections over one extending perpendicular to the double pipe sections Connection bends are connected to each other.

The double tube heat exchanger can preferably be used as a feed water preheater be used for the water to be supplied to the container. In this case the other pipe will have at least part of the double pipe heat exchanger the feed water to be supplied to the container for preheating the Feed water charged.  

On the other hand, it is also possible for the other pipe to have at least one part the double tube heat exchanger with saturated steam removed from the tank is applied to produce superheated steam (superheated steam).

Both options can also be combined by using a Process gas individual flow initially via a saturated steam Double tube heat exchanger and then one with feed water charged double tube heat exchanger is performed.

It is particularly expedient to regulate the gas outlet temperature the gas inlet temperature of everyone from the waste heat boiler Double tube heat exchanger is measured and the measured values averaged and depending on the mean of the Process gas inlet temperatures in the individual double tube heat exchangers the water level in the tank and thus the heat absorption of the pipes in the Container-determining immersion depth of the pipes is regulated.

The invention is also directed to a heat recovery steam generator for generation of steam by means of hot process gases, especially by means of the catalytic fission of hydrocarbons based on the partial Oxidation occurs at high pressures and high temperatures Process gases, with a waste heat boiler including one with water in predetermined height filled standing container, a variety of in Containers arranged and acted upon with the process gases and from pipes and a device for pulling out of saturated steam from the container.

According to the invention, the waste heat steam generator is characterized in that each pipe from the waste heat boiler tank with the one tube of a double tube heat exchanger is connected, the other Pipe with a different fluid flow such. B. water or saturated steam can be acted upon and one pipe of which can be shut off by means of a valve.

The claims 7 to 16 are directed to advantageous embodiments of the Heat recovery steam generator according to the invention.

The inventive method and the inventive Heat recovery steam generators in various embodiments should now will be explained in more detail with reference to the accompanying figures. It shows:

Fig. 1 shows an embodiment of the steam generator according to the invention, in which the individual pipes associated with the waste heat boiler in one double-tube heat exchanger with vertical coaxial double-tube sections, the two heat exchangers are on the gas side and the water side connected in parallel,

Fig. 2 shows a second embodiment of the steam generator according to the invention, wherein individual tubes in the heat recovery steam generator is assigned a double tube heat exchanger with horizontally extending coaxial double tube sections which are on the gas side and the water side connected in parallel,

Fig. 3 shows an embodiment of the steam generator according to the invention, in which the individual pipes in the waste heat boiler are each connected to two double-pipe heat exchangers or sections connected in series on the gas side, of which the first is connected as superheater and the second as feed water preheater, and

Fig. 4 is a section through the double-tube heat exchange assembly according to Fig. 3 in the direction of arrows IV-IV in Fig. 3.

The steam generator shown in FIG. 1 has a waste heat boiler 1 with a standing container, in the water space 2 of which a plurality of candles 3 are arranged. For the sake of simplicity, only two candles 3 and 4 are shown in FIG. 1. Each candle has several tubes that are spirally inserted into each other (candles with only one tube are also possible). For the sake of simplicity, only two tubes 3 a and 3 b are assigned to the candle in FIG. 1, and only two tubes 4 a and 4 b are assigned to the candle 4 . The spirally inserted tubes are each surrounded by a flow control cylinder (jacket) 3 c or 4 c. Each of the spiral tubes is connected to an inlet 3 d and 4 d. These open up to a process gas distribution chamber 5 which is supplied with process gas PG by a reactor (not shown) via a connecting piece 6 .

A water level 7 is maintained in the interior 2 . Feed water is supplied via a distributor 8 along the inner surface of the waste heat boiler and flows into candles 3 and 4 from below (cf. the arrows in the waste heat boiler). Saturated steam SD is withdrawn from the waste heat boiler via an extraction device 9 . In order to achieve particularly good cooling at the entry of the gases into the tubes of the candles 3 and 4 , water cooling in natural circulation is provided in the entry area, on which a forced circulation caused by a pump 10 is superimposed.

The tube 3 a is connected via a connecting line 11 a to a double tube heat exchanger 12 . The double-tube heat exchanger 12 consists of three vertically arranged coaxial double-tube sections 13 , 14 and 15 . The connecting line 11 a is connected to the inner tube 13 a of section 13 . The inner tubes 13 a, 14 a and 15 a of the sections 13 , 14 and 15 are connected to one another via curved sections 16 and 17 in the manner shown in FIG. 1. The arc sections 16 and 17 can be provided on the inside with an erosion protection layer to increase the service life. The bends can also be provided with a greater wall thickness than the straight cylindrical inner tube sections in order to achieve the same effect. The inner tube 15 a is connected to a collector 20 via a line 19 which can be shut off by a valve 18 . The collector 20 is connected via a line 21 to a gas scrubber, not shown.

The outer tubes 13 b, 14 b and 15 b are connected to one another via connecting lines 22 and 23 extending perpendicular to the double tube sections. The outer tube 15 b is supplied with feed water from a distributor 24 loaded with feed water. In the connecting line from the accumulator 24 b to the outer tube 15, a valve 18 is arranged ', the water supply can be throttled to the double-pipe heat exchanger 12 at least with the closure in the associated gas path of the double-pipe heat exchanger valve 18th Such throttling is advantageous in order to prevent that when individual gas paths are shut off due to the pressure loss around the pipes which decreases on the water side, there is too great an imbalance between the heated and unheated lines or paths.

In order to improve the heat transfer coefficient from the process gas to the water, the gas-carrying inner tubes in a preferred embodiment are provided with outer fins, as is shown schematically as outer fins 13 a 'on the inner tube 13 of the double-tube heat exchanger 12 in FIG. 1. (Such external fins can also be used in the embodiment according to FIGS. 3 and 4 in order to improve the heat transfer from the process gas to the steam to be heated). The feed water flows via connecting pipe 23 , outer pipe 14 b, connecting pipe 22 , outer pipe 13 b and via a line 25 to a collector 26 , which is connected via one or more lines to the distributor 8 inside the waste heat boiler 1 .

In a corresponding manner, the pipe 4 is connected to the collector 20 for the process gas, the distributor 24 and the collector 26 for the feed water via a correspondingly designed double-pipe heat exchanger 27 .

The embodiment according to FIG. 2 differs from the embodiment according to FIG. 1 in that the coiled tubes have return lines 4 aa or 3 aa which are led from the upper end of the candle 4 or 3 to the lower end of the candle and that Double pipe sections of the double pipe heat exchangers 12 'and 27 ' extend horizontally, the heat exchanger 27 'like the heat exchanger 27 in FIG. 1 being connected via a line 28 a to the associated pipe 4 a of the candle 4 .

Associated with the tubes 3 b and 4 b in the embodiments of FIG. 1 and FIG. 2 in a corresponding manner, the double-tube heat exchanger.

In the embodiment according to FIGS. 3 and 4, return lines 4 aa and 3 aa are also provided. A double-tube heat exchanger 29 , which consists of a superheater section 30 and a preheating section 31, is connected downstream of each single line or single pipe. The inner pipe of the upper double pipe section 13 of the superheater section 30 is supplied with the process gas via line 28 a, while the outer pipe of the lower double pipe section 15 shown in FIG. 3 is supplied with saturated steam supplied from the extraction device 9 via line 33 via a distributor 32 . The steam superheated in the superheater section 30 is discharged from the outer tube of the upper section 13 of the superheater via a collector 34 and a line 35 .

The process gas leaving the superheater section 30 enters the inner tube of the upper double tube section 13 of the preheating section 31 and is fed to a collector 20 , from which it is led to the gas scrubbing.

The outer pipe of the lower double pipe section 15 of the preheater section 31 is supplied with feed water by a distributor 24 . The preheated feed water drawn off from the upper double pipe section 13 of the preheater 31 is fed via a collector 26 to the distributor 8 in the waste heat boiler. The arrows on the distributors 24 and 32 indicate that the corresponding double-tube heat exchangers for the other individual tubes or strands are supplied with feed water or saturated steam from the waste heat boiler, and the arrows on the collectors 20 , 26 and 34 indicate that Process gases, preheated feed water or superheated steam are collected here.

The tubes 3 a, 3 b and 4 b are each assigned a double tube heat exchanger in a corresponding manner.

Fig. 4 shows a section along the line IV-IV in Fig. 3 to show that the four double-tube heat exchangers 29 , which correspond to the four gas paths only shown for example in the waste heat boiler 1 , can be arranged side by side in a modular manner, the components of each Double tube heat exchanger 29 extend in a vertical plane and the exemplary four heat exchangers are arranged in mutually parallel planes. This leads to an extremely compact design. The modular design also minimizes any replacement times that may be required and / or minimizes spare parts inventory.

Such a compact design can also be achieved when the double tube heat exchangers of FIGS. 1 and 2 are arranged side by side.

The use of straight pipes for the double pipe sections of the Double tube heat exchanger leads to a reduction in all embodiments erosion and thus to a higher availability or service life.  

To regulate the hot gas outlet temperature from the heat boiler, the outlet temperature of the individual strand from the waste heat boiler 1 is recorded by means of individually assigned measuring devices TI. The measured values are averaged in a control device CON. The output signal of a water level measuring device LT is also supplied to this control device CON. If necessary, the control device CON can also be connected to the superheated steam temperature according to collector 34 via a measuring device TIC. The control device CON controls a feed water pump 36 provided in the feed water supply as a function of a predetermined set point in order to set the water level 7 in the boiler and thus the immersion depth of the pipes and thus their heat absorption which determines the gas outlet temperature.

With this procedure, it is useful that the in the control range of Water level possible from the boiling water in the container of the Waste heat boiler protruding part of the spiral heating surface (candle) Stainless steel is made to be a critical when using ferrites Avoid hot water corrosion (flaking of the magnetite protective layer). The The part that is always immersed in water can be made of ferritic material be made.

The trapezoid symbols 37 and 38 in the lines 3 a and 4 b in the waste heat boiler 1 and in the double-tube heat exchangers 12 , 27 , 29 are intended to indicate that a cross-sectional narrowing should take place here in the direction of the gas flow, ie after the smaller trapezoidal cover surface, in order to reduce the flow velocity in the subsequent pipes or pipe sections. The diameters of the following pipes or pipe sections are smaller in accordance with the narrowing of the cross-section, ie a pipe gradation is preferably carried out both in the evaporator (waste heat boiler) and in the double-pipe heat exchangers which form a preheater or a superheater.

The double-line symbols 39 represent so-called spectacle plug-in disks that can be used to adjust the partial load behavior. The symbol 40 used in FIGS. 1 to 3 is intended to indicate that the connecting bends can be flanged to the inner tubes of the coaxial double tube sections in a simple manner.

As described in the introduction to the examples according to FIGS. 1 and 2, the two pipes 19 of the heat exchangers 12, 27 and 12 ', 27' before the process gas collector 20, to which also the other tubes 3 b and 4 b associated double-tube heat exchanger are connected on the gas side, brought together and shut off from the collector by a single valve 18 . There is no purely individual shut-off here, but a simultaneous shut-off of two double-tube heat exchangers, which, compared to a shut-off of a large number of process gas tubes, is also to be regarded as an "individual shut-off" in the sense of the present invention.

Claims (16)

1. A method for generating steam by means of hot process gases, in particular by means of process gases formed in the non-catalytic splitting of hydrocarbons based on the partial oxidation at high pressures and high temperatures, in which the process gases for generating saturated steam in a large number of individual streams by means of pipes a standing container filled with water and withdrawn from it in individual flows and saturated steam discharged from the container, characterized in that the individual process gas flows withdrawn from the container are each conducted to a tube of a double-tube heat exchanger, the other tube of which is acted upon by a different fluid stream , and that at least one tube of the double tube heat exchanger can be shut off on the gas outlet side. 2. The method according to claim 1, characterized, that the other tube is at least part of the Double tube heat exchanger with the one to be fed to the tank Feed water for preheating the feed water is applied. 3. The method according to claim 1 or 2, characterized, that the other tube is at least part of the double tube heat exchanger  with saturated steam withdrawn from the container Generate superheated steam (superheated steam). 4. The method according to at least one of claims 1 to 3, characterized, that a single process gas stream initially via a saturated steam acted upon double tube heat exchanger and then with a Feed water charged double tube heat exchanger is guided. 5. The method according to at least one of claims 1 to 4, characterized, that to control the gas outlet temperature from the waste heat boiler Gas inlet temperature of each double tube heat exchanger measured is and the measured values averaged and depending on the Average of the process gas inlet temperatures in the individual Double tube heat exchanger the water level in the tank and thus the The heat absorption of the pipes in the tank determines the immersion depth Pipes is regulated. 6. Heat recovery steam generator for generating steam by means of hot process gases, in particular by means of process gases arising in the non-catalytic splitting of hydrocarbons based on the partial oxidation at high pressures and high temperatures, with a waste heat boiler including a standing container filled with water at a predetermined height, a large number of Pipes arranged in the tank and loaded with the process gases and led out of the tank and a device for drawing saturated steam out of the tank, characterized in that each pipe ( 3 a, 11 a) led out of the tank of the waste heat boiler with the one pipe ( 13 a, 14 a, 15 a) of a double tube heat exchanger ( 12 ) is connected, the other tube ( 13 b, 14 b, 15 b) can be acted upon by another fluid flow ( 24 ; 32 ) and one tube by means of a valve ( 18 ) is lockable. 7. waste heat steam generator according to claim 4, characterized in that the double-pipe heat exchanger (12; 27; 12 ';27'; 29, 30, 31) coaxial with at least two double tube sections (13, 14; 15) whose inner tube portions (13 a ; 14 a; 15 a) are connected to one another via a connecting bend ( 16 ; 17 ) and their outer pipe sections ( 13 b; 14 b; 15 b) via a connecting pipe ( 22 ; 23 ) extending perpendicular to the double pipe sections. 8. heat recovery steam generator according to claim 6 or 7, characterized in that the inner pipe sections ( 13 a; 14 a; 15 a) with the process gas (PG) and the outer pipe sections ( 13 b; 14 b; 15 b) with the other fluid are acted upon. 9. heat recovery steam generator according to at least one of claims 6 to 8, characterized in that the other tube ( 13 b; 14 b; 15 b; 12 ; 27 ; 12 '; 27 ') with feed water ( 24 ) can be acted upon. 10. heat recovery steam generator according to at least one of claims 6 to 8, characterized in that the other tube ( 13 b; 14 b; 15 ; 30 ) with saturated steam (SD) can be acted upon. 11. Heat recovery steam generator according to at least one of claims 6 to 10, characterized in that two process gas streams associated double tube heat exchangers ( 12 , 27 ; 12 '; 27 ') are connected in parallel both on the process gas side and on the fluid side. 12. Heat recovery steam generator according to at least one of claims 6 to 11, characterized in that a process gas tube ( 4 ; 28 a) with a double-tube heat exchanger or double-tube heat exchanger section ( 30 ) which can be acted on with saturated steam (SD) is connected to the gas side with a double-tube heat exchanger which can be acted on with feed water or double tube heat exchanger section ( 31 ) is connected. 13. Heat recovery steam generator according to at least one of claims 6 to 12, characterized in that the double tube heat exchanger ( 12 '; 27 '; 29 ) are arranged such that their concentric double tube sections ( 13 ; 14 ; 15 ) are vertical ( Fig. 1) or extend horizontally ( Fig. 2; Fig. 3). 14. Heat recovery steam generator according to at least one of claims 6 to 13, characterized in that the concentric double pipe sections ( 13 ; 14 ; 15 ) and their connecting pipes ( 16 , 17 ; 22 , 23 ) of a double pipe heat exchanger are arranged in one plane and a plurality of double pipe heat exchangers ( 12 ; 27 ; 12 '; 27 '; 29 , 30 , 31 ) are combined to form assemblies with mutually parallel planes and the double-tube heat exchanger on the gas outlet side with a common collector ( 20 ) and fluid inlet side and outlet side with common distributors ( 24 ; 32 ) or common Collectors ( 26 ; 34 ) are connected. 15. Heat recovery steam generator according to at least one of claims 6 to 14, characterized in that the tubes ( 3 a, 3 b, 4 a, 4 b) through which the process gases flow are formed as spiral tubes in the waste heat boiler ( 1 ), at least some of which are intertwined in groups. 16. heat recovery steam generator according to at least one of claims 6 to 15, characterized in that the inner tubes ( 13 a, 14 a, 15 a) of the double-tube heat exchanger through which the process gases flow in succession have different smaller ( 38 ) diameters.