EP0170663A1 - Procede pour utiliser la chaleur de reaction lors de la synthese de l'ammoniac - Google Patents

Procede pour utiliser la chaleur de reaction lors de la synthese de l'ammoniac

Info

Publication number
EP0170663A1
EP0170663A1 EP85900620A EP85900620A EP0170663A1 EP 0170663 A1 EP0170663 A1 EP 0170663A1 EP 85900620 A EP85900620 A EP 85900620A EP 85900620 A EP85900620 A EP 85900620A EP 0170663 A1 EP0170663 A1 EP 0170663A1
Authority
EP
European Patent Office
Prior art keywords
ammonia
synthesis
pressure
energy
heat
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP85900620A
Other languages
German (de)
English (en)
Inventor
Ludwig Silberring
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Individual
Original Assignee
Individual
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Individual filed Critical Individual
Publication of EP0170663A1 publication Critical patent/EP0170663A1/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01C—AMMONIA; CYANOGEN; COMPOUNDS THEREOF
    • C01C1/00—Ammonia; Compounds thereof
    • C01C1/02—Preparation, purification or separation of ammonia
    • C01C1/04—Preparation of ammonia by synthesis
    • C01C1/0405—Preparation of ammonia by synthesis from N2 and H2 in presence of a catalyst
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P20/00—Technologies relating to chemical industry
    • Y02P20/50—Improvements relating to the production of bulk chemicals
    • Y02P20/52—Improvements relating to the production of bulk chemicals using catalysts, e.g. selective catalysts

Definitions

  • Ammonia synthesis is currently usually carried out at temperatures between 400 and 500 ° C. Under these conditions, the heat release from the exothermic synthesis reaction is approximately 3.1 J / g. .
  • the following explanations now relate to a specific ammonia synthesis plant with a production capacity of 1000 t per day, i.e. 11.6 kg / s. The total thermal energy which is released in such an ammonia synthesis is approximately 36 MW at the temperatures mentioned.
  • At least part of the heat required to increase the temperature of the synthesis gas to the temperature mentioned is normally recovered from the heat of the reaction products after the converter.
  • the heat capacities of the two streams are not identical. Therefore, the amount of heat usable for other purposes is less than the above 36 MW, namely about 28 MW.
  • the heat released in the ammonia synthesis circuit is usually used today to increase the temperature of the feed water in the usual high-pressure steam circuit of ammonia production plants.
  • other heat sources at relatively low temperatures in ammonia production plants must also be taken into account. Examples of this are the heat which arises during the conversion of carbon monoxide, the heat content of the process gas stream after the conversion mentioned, and the heat content of the excess steam in this process section. Therefore 'importance tet the heating of steam boiler feed water means for synthesis is not necessarily a real heat energy gain.
  • the same Warming up, as mentioned, can be carried out using other available heat sources. This is especially true if a low-energy system is used for the removal of carbon dioxide.
  • part of the heat of synthesis is used to raise the temperature from saturated high-pressure steam to that of other steam sources in the ammonia plant.
  • this type of heat recovery is only insufficiently efficient if the heat exchanger used for this is installed, as usual, in the synthesis gas line after the converter. Because of the restrictions in the temperature difference, only a small part of the heat of the synthesis gases can be reused in this way.
  • the temperature of steam is raised, with the steam pipes placed in the synthesis converter. In this case, good heat recovery is made possible, but this is done by accepting an increased risk by introducing water into the synthesis converter.
  • the ammonia synthesis heat is used in an energy cycle with ammonia as the material.
  • This cycle is shown in two variants using the attached drawings.
  • FIG. 1 the simpler embodiment is shown, which already leads to good energy savings
  • variant 2, FIG. 2 is more complex and leads to an even higher energy efficiency of the system.
  • process' is the chendem at entspre ⁇ bef pressure and approximately room temperature the Synthese Vietnamese ⁇ running taken ammonia at the same high pressure by means of heat for synthesis heated to a temperature of about 360 ° C.
  • the heated ammonia is placed in an expansion machine in which the pressure is reduced to about 14 bar, mechanical energy of the order of magnitude of 5.5 MW being generated.
  • ammonia is condensed by means of cooling water and introduced through a throttle valve into the evaporator of the cooling system at medium pressure. This system works at a pressure of approximately 3 bar.
  • the liquid ammonia together with the small amount of ammonia from the low-pressure cooling system, is then drawn off from the bottom of the said evaporator and, again through a throttle valve, brought to a pressure of approximately 1 bar. At this pressure level, the ammonia vapor is separated off and the liquid ammonia is used for storage or delivered for transport at atmospheric pressure.
  • ammonia vapor from the last-mentioned separator is compressed within the low-pressure cooling system to the pressure level which corresponds to the suction pressure within the medium-pressure cooling system.
  • the ammonia vapor mentioned is combined with that from the evaporator of the medium-pressure cooling system.
  • Both ammonia flows are now compressed by means of the compressor of the system mentioned to that pressure level which corresponds to that of the outlet of the expansion machine mentioned above.
  • the compressed ammonia vapor is combined with the ammonia that comes from the expansion machine mentioned.
  • the combined ammonia flows are now, as already said above, fed to the water-cooled condenser.
  • the liquid ammonia from the synthesis cycle is saturated with synthesis gas.
  • This gas which is released in the water-cooled condenser, is fed to a conventional further treatment system.
  • the mechanical energy which is obtained by means of the ammonia expansion machine is sufficient to drive the cooling compressors of the medium-pressure and the low-pressure cooling system. Electric motors must be provided to drive the compressors, especially for starting the system.
  • the cooling energy of the medium-pressure cooling system is used to condense at least half of the ammonia generated during the synthesis. (The remaining half is usually condensed by means of cooling water.)
  • the low-pressure cooling system is used for cooling the ammonia product to the saturation temperature at ambient pressure.
  • the same cooling system can also be used for the condensation of most of the ammonia in the exhaust gas.
  • only about 20 MW of the heat energy released in the ammonia synthesis is recycled.
  • the remaining heat energy can be used for other purposes, but it can also be removed using cooling water.
  • the most important characteristic of variant 1, compared to variant 2 described below, is its simplicity. On the other hand, the mechanical energy gained is just enough to drive the cooling compressors.
  • Variant 2 is a little more complex and allows an increased energy gain of around 3 MW compared to variant 1. This is achieved by increasing the ammonia flow through the heat recovery system and through the expansion machine. The additional ammonia required for this is introduced from the water-cooled condenser into this recovery system by means of a high-pressure pump. In addition, an aggregate is also required for preheating the liquid ammonia in order to increase the efficiency of the entire circuit.
  • the total thermal energy of the ammonia synthesis i.e. 28 MW, required to heat ammonia to the same temperature as in variant 1.
  • the higher mass flow through the expansion machine leads to a higher mechanical output, namely approximately 8.5 MW.
  • the other elements of variant 2 are identical to those of variant 1.
  • ammonia as the working substance eliminates the need to introduce any foreign substances into one or more elements of the ammonia synthesis cycle. This will make security of the operation of the plant increased.
  • the ammonia accumulates at a high pressure level, equal to the pressure within the synthesis cycle. At least in variant 1, therefore, no high-pressure pumps are necessary for the proposed energy recovery system.
  • ammonia expansion machine with the ammonia compressors for cooling allows the construction of compact units which also only have one and the same working medium. All shaft sealing systems can be tuned to the lowest pressure, which is approximately atmospheric pressure.
  • variant 2 only about 40% of the ammonia of the recovery system has to be returned to the expansion machine by means of high-pressure pumps.
  • the energy required for this is approximately 0.4 MW; the net energy gain compared to variant 1 is therefore still over 2 , 6 MW.
  • the pressure of the ammonia in the ammonia energy cycle system is the same as the pressure in the ammonia synthesis! Oop.
  • the ammonia heater in the ammonia converter is therefore not exposed to any significant pressure difference. It must be noted here that this pressure equality is inherent in the system and does not have to be achieved by means of artificial means, such as pressure compensation devices. In fact, the pressure difference is simply checked by the ammonia heater by means of the inlet valve in the ammonia expansion machine. Therefore, the calculation pressure difference for the two sides of the ammonia heater is at very low values and leads to massive wall thicknesses of the apparatus.
  • ammonia is heated at a pressure that is far below its critical pressure. Therefore, the ammonia heater becomes a "once-through type", i.e. an apparatus with a single passage of the ammonia.
  • the heat exchanger will have a number of thin, parallel pipes.
  • the temperature of the superheated ammonia does not have to be checked, since the value of the ammonia is not very high and in any case never exceeds the temperature in the converter; the last-mentioned temperature is also known to be not very high.
  • ammonia heater within the ammonia converter is a very simple apparatus that does not require any important auxiliary equipment.
  • the heater allows the control of the synthesis gas temperature inside the converter in a much better way than all of them previously known systems.
  • a detailed description of the construction drawings lies outside of this specification.
  • the heating of ammonia to a temperature of 360 ° C. according to the invention must also be discussed with regard to the thermal stability of ammonia. From the standpoint of the thermodynamic equilibrium conditions between ammonia and synthesis gas, ammonia is not very stable even at room temperature. However, the decomposition of ammonia also proceeds slowly at the temperatures under consideration, so that at least one can speak of technically sufficient stability. However, one must look at the absolute absence of elements that have a catalytic effect. Therefore, all metal surfaces with which the ammonia comes into contact at the temperatures mentioned must be very well pass. Likewise, it should be ensured that the Kontak Ttime not contribute 'by Ammo ⁇ niak at the high temperatures more than a few seconds be ⁇ .
  • the rate of decomposition is negligible.
  • the upper process temperature can be reduced. For example, a reduction in the upper temperature from 360 to 300 ° C would only lead to a reduction in the mechanical energy gain by approximately 0.6 MW. The advantages of the new method would not be significantly reduced even under these restricted conditions.
  • Gas expansion machines are well known in the process industries. They are normally used to obtain mechanical energy in those process steps where gas flows have to be subjected to a pressure reduction. A sufficiently large experience is therefore available to provide the thermodynamic, hydrodynamic and mechanical construction principles. However, it should be noted here that there is at least one quantitative difference between the known machines and that for the process described here. In particular, the gas inlet pressure is significantly higher than in most cases of known expansion machines and the performance of the new machine is also considerably higher. A specific new construction will therefore be required for the ammonia expansion machine, which is required for the process according to the invention.
  • the most suitable machine will most likely be one of the centripetal turboexpander type.
  • the machine will be somewhat similar to those which are known from low-temperature technology. At least 2 stages will be required to avoid supersonic speeds of ammonia. The division of the machine into two stages will also allow the extraction of ammonia, which is necessary according to variant 2.
  • the rotational speed of the expansion machine is matched to that of the driven device whenever possible. Seals on the high-pressure side of the rotor should preferably be avoided. If such are nevertheless necessary, such seals can be lubricated with ammonia to avoid the need for high pressure seals. Escaping ammonia vapors can also be easily recovered even in cases where high-pressure seals are selected. This applies particularly to those cases in which the energy obtained in the expansion machine is used to drive the refrigeration compressors.
  • the energy which is obtained in the expansion machine described above can in principle be used anywhere and for any purpose. The best use is of course that within the plant and as close as possible to the ammonia synthesis. cycle.
  • the recovered energy is not sufficient to supply the starting gas mixture entering the converter. ompress. But the energy is more than enough to drive all compressors and pumps in the cooling devices for the ammonia synthesis cycle.
  • this use is explained as an example in the variants 1 and 2 described above.
  • the ammonia expansion systems can be connected directly to the cooling compressors by means of a common shaft. As already mentioned, a common shaft sealing system can be used.
  • start-up rotor is therefore advantageously connected to the expansion machine-cooling compressor combination described above.
  • the same motor can also be used for any additional power that may be required.
  • the energy requirement for a modern ammonia production plant expressed on the basis of the lower calorific value of the materials used, can be roughly divided into two parts: first, the raw materials, for which approximately 2/3 of the energy is required, and then secondly in fuel, which makes up approximately the remaining third of the energy required.
  • the method described above allows a reduction in the amount of fuel required of approximately 20%.

Landscapes

  • Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Analytical Chemistry (AREA)
  • Inorganic Chemistry (AREA)
  • Engine Equipment That Uses Special Cycles (AREA)

Abstract

Lors de la synthèse de l'ammoniac, la chaleur de réaction libérée peut être utilisée dans un circuit dont le fluide de travail est l'ammoniac. Dans une unité de production d'ammoniac d'une capacité de 1.000 tonnes par jour, on peut de cette manière obtenir une puissance mécanique de 8,5 MW. L'énergie obtenue peut être avantageusement utilisée pour actionner les compresseurs de refroidissement. On peut obtenir une économie globale de 20% en carburant par rapport aux installations actuelles. Le procédé améliore la sécurité de l'unité et simplifie son exploitation.
EP85900620A 1984-02-13 1985-02-07 Procede pour utiliser la chaleur de reaction lors de la synthese de l'ammoniac Withdrawn EP0170663A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
CH670/84 1984-02-13
CH67084 1984-02-13

Publications (1)

Publication Number Publication Date
EP0170663A1 true EP0170663A1 (fr) 1986-02-12

Family

ID=4192416

Family Applications (1)

Application Number Title Priority Date Filing Date
EP85900620A Withdrawn EP0170663A1 (fr) 1984-02-13 1985-02-07 Procede pour utiliser la chaleur de reaction lors de la synthese de l'ammoniac

Country Status (2)

Country Link
EP (1) EP0170663A1 (fr)
WO (1) WO1985003501A1 (fr)

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE1258851B (de) * 1964-09-18 1968-01-18 Zaklady Azotowe Kedzierzyn Fa Verfahren und Vorrichtung zur Kuehlung der Reaktionsgase bei der Ammoniaksynthese
FR1490618A (fr) * 1966-06-20 1967-08-04 Azote & Prod Chim Procédé de récupération d'énergie dans les installations de synthèse de l'ammoniac
CH500006A (de) * 1968-08-23 1970-12-15 Escher Wyss Ag Syntheseanlage
DE3109393A1 (de) * 1981-03-12 1982-12-02 Karl Prof. Dr.phil. Dr.-Ing.h.c. 8730 Bad Kissingen Schoenemann Verfahren zur nutzung der reaktionsenthalpie exothermer heterogen-katalytischer gasreaktionen

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO8503501A1 *

Also Published As

Publication number Publication date
WO1985003501A1 (fr) 1985-08-15

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