Method for thermally after-burning waste gases from acrolein and hydrocyanic acid production

Abstract

The invention relates to a method for thermally after-burning the waste gas flows developing during the production of acrolein in a gas phase process and for thermally after-burning the waste gas flows developing during the production of hydrocyanic acid in a gas phase process, characterized in that the waste gas flows from the production of acrolein and the waste gas flows from the production of hydrocyanic acid are supplied to a joint thermal after-burning process.

Claims

1. A process for thermal afterburning, comprising forming an exhaust gas stream in the production of acrolein in a gas-phase process, wherein the exhaust gas stream arising in the production of acrolein in a gas-phase process comprises an exhaust gas stream from a process of gas-phase oxidation of propylene to acrolein, forming an exhaust gas stream in the production of prussic acid in a gas-phase process, wherein the exhaust gas stream arising in the production of prussic acid in a gas-phase process comprises an exhaust gas stream from an Andrussow process or from a BMAprussic acid from methane and ammoniaprocess; feeding the exhaust gas stream from the production of acrolein and the exhaust gas stream from the production of prussic acid to a shared thermal afterburning; and burning the exhaust gas stream from the production of acrolein and the exhaust gas stream from the production of prussic acid in the shared thermal afterburning.

2. The process of claim 1, wherein the production of acrolein and the production of prussic acid take place in parallel with respect to time, and the exhaust gas stream from the production of acrolein and the exhaust gas stream from the production of prussic acid arise in parallel with respect to time.

3. The process of claim 1, wherein the production of acrolein and the production of prussic acid take place at one location, and the exhaust gas stream from the production of acrolein and the exhaust gas stream from the production of prussic acid arise at one location.

4. The process of claim 1, wherein the shared thermal afterburning comprises an integrated process for chemical synthesis of methionine or methionine hydroxy analogue (MHA).

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1 illustrates a process for production of acrolein.

(2) FIG. 2 illustrates a process for the production of prussic acid.

(3) FIG. 3 illustrates schematically acrolein and prussic acid production according to the invention.

(4) This object is achieved by a process for the thermal afterburning of the exhaust gas streams that are formed in the production of acrolein in a gas-phase process, and the thermal afterburning of the exhaust gas streams that are formed in the production of prussic acid in a gas-phase process, characterized in that the exhaust gas streams from the production of acrolein and the exhaust gas streams from the production of prussic acid are fed to a shared thermal afterburning.

(5) The exhaust gas streams are therefore not disposed of separately in separate processes, but both exhaust gas streams are treated in a single thermal afterburning. The thermal afterburning of the exhaust gas streams from the production of acrolein and from the production of prussic acid also does not proceed successively with respect to time, but at least partially in parallel with respect to time, i.e. concurrently with respect to time.

(6) Preferably, the exhaust gas streams are fed to the thermal afterburning with the greatest possible overlapping in time. For this purpose, the exhaust gas streams from the production of acrolein and the exhaust gas streams from the production of prussic acid can first be combined and fed together to the thermal afterburning, or each exhaust gas stream can be fed separately in parallel, assuming that this does not proceed sequentially in time, but at least partially parallel in time, i.e. concurrently with respect to time.

(7) In a preferred embodiment of the process according to the present invention, not only the exhaust gas stream arising in the acrolein production, but also the resultant wastewater stream is fed to the thermal afterburning. As a result, a biological treatment stage for the resultant wastewater can be dispensed with.

(8) A shared combustion plant for both process exhaust gases, owing to upscaling effects, would already offer the customary savings on capital expenditure for such a plant, since two combustion plants do not need to be built, but only one individual combustion plant dimensioned to be correspondingly larger therefor.

(9) However, completely surprisingly, it has been found that a shared thermal afterburning is associated with further substantial advantages.

(10) The shared thermal afterburning makes possible a lower introduction of air. As a result smaller amounts of nitrogen which do not have a calorific value are introduced. Less nitrogen from the air needs to be heated, which leads to a lower heat loss. Therefore, the steam production, based on the additional fuel used, increases.

(11) The reason for the savings in combustion air is in the composition of the two exhaust gas streams. The exhaust gas stream from the production of acrolein has a relatively low calorific value, but still contains significant concentrations of residual oxygen (see Table 1). The exhaust gas stream from the production of prussic acid contains excess calorific value, but virtually no more oxygen (see Table 2). Some of the oxygen required for the combustion of the exhaust gas from the production of prussic acid can be provided via the shared thermal afterburning by the exhaust gas stream from the production of acrolein. Since less combustion air is required, in the shared thermal afterburning, a smaller combustion chamber volume can also be used, than would be possible in the case of a simple design without synergistic effects.

(12) A further advantage of the process according to the invention is the saving of additional fuel. Since the exhaust gas stream from the production of prussic acid contains excess calorific value, the exhaust gas stream from the production of prussic acid replaces at least in part the feed of additional fuel.

(13) Preferably, the process according to the invention is distinguished in that the exhaust gas streams arising in the production of prussic acid in a gas-phase process are exhaust gas streams from the Andrussow process. The Andrussow process is known to those skilled in the art and is described by way of example in Ullmann's Encyclopedia of Industrial Chemistry, sixth Edition, Volume 10, page 194. In a further preferred embodiment of the process according to the invention, the exhaust gas streams arising in the production of prussic acid in a gas-phase process are exhaust gas streams from the BMAprussic acid from methane and ammoniaprocess. This process is also known to those skilled in the art and is also described by way of example in Ullmann's Encyclopedia of Industrial Chemistry, sixth Edition, Volume 10, page 194.

(14) Preferably, the process according to the invention is also distinguished in that the exhaust gas streams arising in the production of acrolein in a gas-phase process are exhaust gas streams from the gas-phase oxidation of propylene to acrolein.

(15) Likewise, preferably, the process according to the invention is also distinguished in that the exhaust gas streams arising in the production of acrolein in a gas-phase process are exhaust gas streams from the gas phase partial oxidation of propane to acrolein.

(16) It is particularly preferred that the exhaust gas streams from the production of acrolein and the production of prussic acid occur in good concurrence with respect to time, in such a manner that the advantages of the shared combustion can be comprehensively utilized without a temporary store for the exhaust gas streams being necessary therefor. The process according to the invention is therefore preferably distinguished in that the production of acrolein and the production of prussic acid take place in parallel with respect to time, and therefore the exhaust gas streams from the production of acrolein and the production of prussic acid likewise arise in parallel with respect to time.

(17) For the optimal utilization of the advantages of a shared disposal of the process exhaust gases, erection and operation on a shared location (group location) is particularly preferred. The process according to the invention is therefore preferably distinguished in that the production of acrolein and the production of prussic acid take place at one location and therefore the exhaust gas streams from the production of acrolein and the production of prussic acid likewise arise at one location. Transport of the exhaust gas streams is thereby minimized and the exhaust gas streams can be fed directly to the thermal afterburning.

(18) In a very particularly preferred embodiment of the process according to the invention, the exhaust gas streams of the production of acrolein and the production of prussic acid arise in good concurrence with respect to time, i.e. parallel with respect to time and at one location.

(19) In FIG. 3 hereinafter, this particularly preferred embodiment of the process according to the invention is shown schematically.

(20) In FIG. 3, the combustion of wastewater from the production of acrolein is also shown. This is optional. The advantages of the process according to the invention still occur when the wastewater of the acrolein process is disposed of separately from the thermal afterburning, for example in a biological wastewater treatment stage.

(21) Further options relate to the process step designated Additional process in FIG. 3. In the context of the invention, it is irrelevant whether this additional process is a classical absorber-desorber unit, in which acrolein or prussic acid is isolated, or whether it is a reactive absorber, in which acrolein or prussic acid can be converted directly into the next intermediate.

(22) In particular, when acrolein and prussic acid are used as precursors for the chemical synthesis of methionine or methionine hydroxy analogue (MHA), the process according to the invention can be used particularly advantageously.

(23) The precursors acrolein and prussic acid are coupled to one another via the end product methionine or methionine hydroxy analogue (MHA). The production of acrolein and the production of prussic acid proceed here in parallel at a shared location, therefore the exhaust gas streams from the production of acrolein and from the production of prussic acid also occur in parallel in time.

(24) In addition, owing to the stoichiometry of the methionine synthesis, quantitative streams for the starting materials acrolein and prussic acid and therefore also exhaust gas streams result which supplement one another expediently with respect to shared thermal afterburning.

(25) The process according to the invention is therefore preferably characterized in that the thermal afterburning is carried out in the context of an integrated process for chemical synthesis of methionine or methionine hydroxy analogue (MHA).

(26) The advantages of the present invention will be described in more detail with reference to the exemplary embodiment hereinafter.

(27) In the production of acrolein (approximately 8 t/h) by gas-phase oxidation of propylene to acrolein, a wastewater stream and exhaust gas stream arise having the following components and amounts:

(28) TABLE-US-00003 TABLE 3 Composition and mass flow rate of the exhaust gas and the wastewater from the acrolein synthesis. Mass flow rate [kg/h] AC wastewater AC exhaust (optional) gas O.sub.2 0 1850 N.sub.2 0 26988 CO 0 180 CO.sub.2 0 674 H.sub.2O 5630 149 Combustible residue (e.g. 1335 132 propene, acrolein, acrylic acid) 6965 29974

(29) For the thermal afterburning of the exhaust gas stream stated under Table 3, approximately 29 550 Nm.sup.3/h of air and 1929 Nm.sup.3/h of natural gas were required. The resultant heat was utilized for steam production, wherein, at the amounts used, approximately 31 t/h of steam (20 bar) were produced.

(30) In the production of prussic acid (approximately 4 t/h) in a gas-phase process by the Andrussow process, an exhaust gas stream arises having the following components and amounts:

(31) TABLE-US-00004 TABLE 4 Composition of the exhaust gas from the production of prussic acid Mass flow rate [kg/h] HCN exhaust gas O.sub.2 152 N.sub.2 27075 CO 2120 CO.sub.2 197 H.sub.2O 186 Combustible residue (e.g. 646 methane, prussic acid, hydrogen) 30376

(32) For the thermal afterburning of the exhaust gas stream stated under Table 4, approximately 27 365 Nm.sup.3/h of air were required. Owing to the thermally utilizable substances present in the exhaust gas stream such as, e.g., methane or hydrogen, an additional feed of natural gas for the thermal afterburning of the exhaust gas from the production of prussic acid was not necessary. The heat produced in the thermal afterburning was utilized for steam production, wherein, at the amounts used, approximately 29.4 t/h of steam (20 bar) could be produced.

(33) The total components and quantitative streams which were fed to the shared afterburning according to the present invention are shown in Table 5.

(34) TABLE-US-00005 TABLE 5 Totality of the exhaust gas and wastewater streams fed to the shared thermal afterburning. Mass flow rate [kg/h] AC AC HCN wastewater exhaust exhaust (optional) gas gas O.sub.2 0 1850 152 N.sub.2 0 26988 27075 CO 0 180 2120 CO.sub.2 0 674 197 H.sub.2O 5630 149 186 Combustible residue (e.g. 1335 132 646 propene, acrolein, acrylic acid, methane, prussic acid, hydrogen) 6965 29974 30376

(35) The thermal afterburning was performed in each case with a residual oxygen content of 3% by volume. The residence time was in each case approximately 2 s. Preheating of the feed gas did not take place. Feed gas is taken to mean all gases which are fed to the thermal afterburning, i.e. not only the process exhaust gases, but also the combustion air and the additional fuel. The combustion temperature was approximately 1130 C. in the case of combustion of the exhaust gas from the production of prussic acid (Tab. 4). In the two other cases (Tab. 3 and Tab. 5), the combustion temperature was accordingly 950 C.

(36) For the shared thermal afterburning of the wastewater and exhaust gas streams stated under Table 5, approximately 46 406 Nm.sup.3/h of air were required.

(37) For the separate thermal afterburning, the following amount of combustion air was required:

(38) 27 365 Nm.sup.3/h+29 550 Nm.sup.3/h=56 915 Nm.sup.3/h

(39) The shared combustion of these two process exhaust gases is proved to enable a reduction of the required combustion air by 18.5%.

(40) For the shared thermal afterburning of the wastewater and exhaust gas streams stated under Table 5, in addition approximately 1158 Nm.sup.3/h of natural gas were required.

(41) For the separate thermal afterburning, 1929 Nm.sup.3/h of natural gas were required.

(42) The shared combustion of these two process exhaust gases makes possible reduction of the required amount of natural gas by 40%. This corresponds to a saving of approximately 200 Nm.sup.3.sub.CH4/t.sub.HCN in the mass flow rates disclosed in the present exemplary embodiment.

(43) The steam production was 51.1 t/h

(44) By means of the process according to the invention, the advantages stated below may be utilized: 1. Scale-up effect owing to the erection and operation of a shared disposal facility, instead of customarily two. 2. Further advantages of the shared combustion of the process gases from acrolein and prussic acid are: a. decreased flue gas volumetric stream b. decreased size of the disposal facility, in such a manner that the capital cost is reduced beyond the abovementioned scale-up effect c. decreased fuel consumption d. decreased fan output for the combustion air e. decreased CO.sub.2 output f. avoidance of possibly excess process steam.