DD280744A1 - METHOD FOR THE COMPLEX UTILIZATION OF ENERGY AND MATERIALS FROM EXHAUST GASES OF THE THERMAL MGC1 DEEP 2-CORE - Google Patents

Abstract

The invention includes a method for the complex use of energy and recyclables from exhaust gases of thermal MgCl2 cleavage. It refers to the treatment of exhaust gases in terms of better utilization of valuable and energy contents in MgO production from MgCl2 noble brine according to the principle of thermal fission. The aim and object of the invention is to integrate the fission gases, which occur in the thermal MgCl2 cleavage, more effectively in the overall process. According to the invention, the object is achieved by adding to the scrubbing tower a subset of the MgSO.sub.4-containing MgCl.sub.2 noble brine to be used for dewatering the cleavage gases, using this solution after neutralization and CaSO.sub.4 precipitation in the cleavage process and highly concentrated it from the thus treated cleavage gases Hydrochloric acid is produced.

Description

For this 1 page drawings

Field of application of the invention

The invention can be applied to the MgO-Horstellung according to the principle of thermal decomposition both in the processing of MgCl ₂ -containing waste brines of Kalirohsalzverarbeitung as well as in the processing of synthetic by hydrochloric digestion of raw magnesite or Magnesitstäuban produce MgC ^ solutions.

Characteristics of the known prior art

The thermal cracking processes are generally operated so that the MgCl ₂ solution to be processed is contacted directly with hot gases from an upstream hot gas generator, whereby the magnesium chloride is converted to magnesium oxide and hydrogen chloride.

From the actual fission reactor usually downstream mechanical emission control system occurs in the use of MgCl ₂ solutions in the cleavage process, which have their origin in Kalirohsalzverarbeitungsprozeß, a cracking gas, the still dusty ingredients in the form of MgO, MgCl ₂ , alkali chlorides and other impurities and contains significant amounts of water vapor.

In the thermal cleavage process, it is in fact so that the resulting hydrogen chloride is regarded as inevitably accumulating accompanying component. However, in order to make the process as a whole economically, it is necessary that a high yield of both components of the MgCl ₂ in the form of MgO and HCl is desired, other material losses in the form of MgCl _{2 are} not allowed and a high degree of heat utilization is sought. For further processing and sales of hydrochloric acid, it is necessary that it is always produced with the highest possible concentration. From the patent literature, several proposals for solving the problem are known, which, however, do not represent a satisfactory solution for all applications.

DD WP 86808 proposes supplying the hot exhaust gases obtained after the mechanical exhaust gas purification to a suitable apparatus, for example a column, these exhaust gases being contacted by the starting solution necessary for the cleavage process. In addition to preconcentration of the solution, dust washing out of the exhaust gas takes place. This procedure has the disadvantage that the cleavage gas with the water removed from the solution further diluted by the resulting water vapor, and thus the production of a highly concentrated hydrochloric acid in the subsequent absorption process is impossible. The method works virtually without repelling solutions, but has the further disadvantage that the impurities contained in the solution can leave the process exclusively on the finished product, and in addition by the rigid coupling reactor pre-concentrator the known difficulties in the control of the process occur. Derived from DD WP 86808 are DD WP 87773 and DD WP 88522.

According to DD WP 87773 takes place after concentration of the dilute, contaminated MgCl ₂ solution in a scrubbing tower, the complete work-up such that it is neutralized by means of lime or dolomite, the HCl content is set equivalent, the sulfate content in the solution. The neutralization with the formation of CaCl ₂ immediately follows the desulfurization. Thereafter, the precipitated calcium sulfate is removed by clarification and filtration. When the solution is cooled, alkali chlorides still precipitate.

The above-mentioned disadvantage for the production of concentrated hydrochloric acid remains. Furthermore, the workup is a total of equipment very expensive and costly. It should be noted, however, that this is a contaminated input solution. In e nzelnen must also be pointed out that the cooling of the circuit with the cold solution from a stacking tank provides a certain rule possibility, however, the required adjustment of the temperature and the concentration of MgCl ₂ and HCI before the neutralization / desulfurization by adding H ₂ O and / or hydrochloric acid and warming takes place. From an operational or production point of view, this represents a variant that is not or hardly controllable.

According to DD WP 88522 is only mentioned in addition to the fact that the HCI absorption should be adiabatic and the further workup to dry hydrogen chloride by means of solution distillation. A similar procedure is of course also required in all these variants when it is necessary to produce a hydrochloric acid of higher concentration than is possible primarily by adiabatic absorption. The method is practically applied to the single-stage Ruthner method described in AT PS 340365 and in the journal Materials and Corrosion, 18 (1967), No. 8, p. 678, but here for FeCla work-up, the hydrochloric acid concentration of subordinate Meaning is.

In DD WP 30390 it is proposed., Pass the obtained after the mechanical exhaust gas purification cracking gas a scrubbing tower, in which the exhaust contact with cooled circulation solution and thereby a Teilkondenssion of water vapor is obtained from the exhaust gas in addition to the cooling of the exhaust gas. The exhaust gas is thus dedusted and dewatered at the same time, which is a great advantage for the subsequent absorption. The irrigation fluid should be such that it can dehydrate the gas without dissolving significant amounts of hydrogen chloride. The resulting in the partial condensation dos water vapor and the exhaust gas cooling heat is discharged via external heat exchanger to a coolant. The excess wash tower solution is removed. Nothing is said about the use of this solution. The usual practice is to discard this solution, which is associated with high energy and material losses. The major disadvantage of this method, however, is that the gas drainage is always bound to a certain amount of dust entering the scrubbing tower.

The process completely fails when the wash tower is preceded by a high-quality mechanical separation plant. The consequence is that the cracked gas can no longer be sufficiently dehydrated and thus only a low-concentrated hydrochloric acid can be produced, which then also has to be fed to an HCl concentration stage. This is the above-mentioned solution distillation by means of MgCl ₂ or CaCl ₂ .

In addition, the discarding of the wash tower solution, whereby previously oine wastewater neutralization must be carried out, in both cases, thus n & chteilig in terms of recyclable material of the components magnesium and chlorine. In the first case (MgCl ₂ abundant), a solution slightly concentrated in MgCl ₂ is obtained, which contains less HCl, in the second case it is the other way around. Correspondingly, the repulsion volumes also vary.

In DD WP 61793 the use of the excess scrubbing tower solution for the production of dry hydrogen chloride is proposed as part of the solution distillation. However, this is only of interest, even if concentrated hydrochloric acid is to be produced directly by absorption. According to DD WP 117433, a method is known to supply these accumulating scrubbing solution of use such that these hydrochloric acid solutions are neutralized with calcium or magnesium compounds and verv in the cleavage process itself for desulphation of the feed solution or for the production of antifreeze. be indet. The underlying this process MgCl ₂ -5paltprozeß is based on a potash final liquor, which is prepared accordingly. In the meantime, the prior art relates to the use of so-called noble sols (MgCl ₂ content: 400 to 460 g / l) produced in external locations in the MgCl ₂ splitting process, which are produced, for example, according to DD WP 200272, and in contrast to the potash end liquor have a lower content of impurities and a higher concentration of MgCl ₂ . This procedure has proven itself.

Object of the invention

The invention aims to achieve a high recovery of valuable material while ensuring the quality of the hydrochloric acid to be produced with respect to the hydrogen chloride content in the MgCl ₂ splitting process, the heat efficiency of the splitting process additionally being improved.

Explanation of the essence of the invention

The invention has the object to ensure the production of highly concentrated hydrochloric acid from the resulting after the thermal cracking cracking gases under various driving conditions of the scrubbing tower, and at the same time to improve the conditions for the Frischlösungsaufbereitung regarding desulfating and subsequent CaSO ₄ removal from the solution.

The invention assumes that a so-called noble brine is used with a MgCl ₂ content of 400 to 460 g / l, an alkali metal chloride content of about 10 g / l and a MgSO ₄ content of about 20 g / l for the cleavage process as starting solution. According to the invention the object is achieved in that the scrubbing tower downstream of the mechanical separation plant in which the Abyas is to be cooled and dewatered, a subset of the MgSO ₄ -containing fresh solution to be used for the cleavage process is supplied in the form of the so-called noble brine. The subset makes up 50 to 95% of the total fresh solution required for the process. Thus, the absolutely essential for the production of highly concentrated hydrochloric acid drainage of the exhaust gas is controlled under all operating conditions by varying the amount of feed into the scrubbing tower reliably, even if the dust input into the scrubbing tower is extremely low. Thus, an almost complete separation of the finished product from the split gas stream can be realized without loss of concentration must be accepted in the production of hydrochloric acid.

The mixture of heated and diluted by the water absorption noble brine including the formed by the registered dust excess washing solution is removed from the washing circuit.

The circulation solution of the scrubber is cooled as already known by means of external heat exchangers indirectly to the required inlet temperature. In this case, according to the invention, a part of the heat exchanger is acted upon by the remaining remainder of the cold fresh solution in the form of the so-called noble brine. Consequently, the MgCl ₂ solution required for the cleavage process consists of the MgC guided over the scrubbing tower! ₂ solution and the guided over the external heat exchanger MgCl ₂ solutions together. However, given the need for external consumers, such as for Bischoffitherstellung, it is also possible to increase these amounts of MgCl ₂ solution beyond the need in the cleavage process, whereby the overall thermal efficiency is positively influenced

The scrubbing solution running out of the scrubbing tower is neutralized with calcium compounds when hot. A part or the total amount of this now still CaCI ₂ contained neutralized still hot scrubbing solution is mixed with the partial flow of the guided via the external heat exchanger fresh solution. By this procedure according to the invention, the desulfurization can now be carried out in the hot state to form CaSO ₄ , which is separated in the subsequent hot-clarifying process. The clarified solution is fed to a treatment process not described in more detail here for the purpose of further purification and optionally concentration.

In order to have the necessary CaCl ₂ amount after implementation of the hydrogen chloride contained in the scrubbing solution with calcium compounds for desulphating the fresh solution at all times, the driving style of the scrubbing tower by varying the abandoned noble oil amount and at the same time by regulating the heat output of the scrubbing tower solution in the external heat exchangers adjusted to the required HCI content.

The advantage is that the regulation of the temperatures and concentrations in the scrubbing tower is controlled within wide limits. The application of the invention is particularly advantageous if the washing tower is preceded by a high-quality mechanical separation plant, since in the thermal fission process must be sought to separate the once-split solid finished product as completely as possible from Spaltnasstrom. Thus, little dust enters the scrubbing tower, thereby making it impossible to form the necessary amount of scrubbing solution for exhaust gas dewatering in such a concentration that little HCI is dissolved.

By feeding a portion of the fresh solution in the scrubbing tower and the supply of the other part to the external heat exchanger, the subsets are variable, the result is the gosamte fresh solution in the hot state, which has a very beneficial effect on the desulphation and the clarification process. As a further advantage results in the cooling circuit a saving of cooling medium. The addition of additional cold solution in the scrubbing tower has the desired effect that the cleavage gas is deprived of a certain amount of heat to heat the solution, which then does not have to be dissipated via the external heat exchanger. As low has been found in practice that the ground limestone is mashed with fresh solution in a neutralization prior to the stirred reactor. In order to allow the lowest possible temperature losses, this fresh solution from the preheated via the heat exchanger / recuperator partial flow is branched. If the ground limestone is directly associated with the hot scrubber solution, there is an exhaust problem such that HCI and fine lime foam are entrained with the escaping CO ₂ from the neutralization. The lime dust complicates the otherwise simple and easy exhaust treatment. It is also beneficial, in addition to limestone and partially use MgO and MgCl ₂ -containing crushed approaches from the thermal cleavage reactors. In extreme Entwäss.trungsvarianten the gas is on the one hand part of the HCI from the wash tower solution virtually free of waste material, on the other hand arises in the neutralization using MgO-containing solids no CO ₂ .

At the same time there is an elegant workup of the approaches that can be mixed in the interest of high MgO product purity only in the rarest cases the final product: Furthermore, it has proved to be advantageous to carry out the neutralization and desulfurization in two series-connected stirred reactors. This is due in particular to the kinetics of the reactions and their complete degree of conversion, both the neutralization and also the precipitation of a CaSO ₄ structure which is favorable for dio clarification and filtration. Thus, the method advantageous according to the invention is in contrast to the

Hitherto known methods in total characterized by a high degree of thermal utilization and at the same time by a high dewatering capacity of the circulated Waschturmiösung relative to the exhaust gas of the thermal MgCl _a cleavage. Thus, it is also possible to carry out the neutralization and the desulfurization under favorable temperature and concentration conditions and to produce a CaSO ₄ with good clarifying and filtering properties. As a result of the designed heating of the entire fresh solution, a desulphated and clarified hot MgCl ₂ solution is obtained, which can be conveniently processed further or fed directly to the MgO process.

MgO-containing mixtures should be used without additional processing stages for neutralization. With only a slight attack MgO-containing approaches part of the purified hot solution for external purposes outside the actual MgO process is used. This or even a certain repulsion of the solution is clearly more advantageous due to the high efficiency than a deficient mechanical separation in the MgO process before the scrubbing tower.

embodiment

FIG. 1

The raw brine I (desulphated noble brine) is proportionally applied to the scrubbing tower 1 or the recuperator 3 used for cooling the circulating solution VIII for the purpose of preheating.

If necessary, the recirculation or recirculation solution is cooled down further in the recuperator 2 by means of cooling water IV. The crude solution is after passing through the recuperator 3 as v / poor solution to a small part of the stirred reactor 5, in which the milled limestone IX is mashed, fed in the main stream but the stirred reactor 6, in which the desulfurization takes place. This is achieved by mixing and neutralizing the wash tower solution / effluent solution VII, which is a hot, HCl-containing MgCl ₂ solution, in the stirred reactor 4 with the warm limestone suspension from the stirred reactor 5 and being removed as excess. The conversion into the stirred reactor 6 is carried out for desulfurization of the preheated partial stream of the crude solution, while the desulfurization of MgSO ₄ portions of the run on the scrubbing tower 1 or via the stirred reactor 5 crude solution already used directly in the neutralization (CaCl ₂ formation) in the stirred reactor 4 , In the hot clarifier 7, the separation of the sewage sludge Vl takes place, mainly in the form of CaSO ₄ , while the hot, clarified solution V is supplied to the further preparation process. Thus, the hot, dust-containing exhaust gas Il cooled from the thermal MgCl ₂ cleavage, dedusted and dewatered III so that it can be passed after passing through the scrubbing tower 1 in the treatment of the scrubbing tower solution according to the invention for HCI absorption. The advantages of the process can best be characterized by the following mass flow and concentration ratios: The exhaust gas of a two-stage thermal MgCl ₂ splitting plant is characterized as follows:

volume fraction

H ₂ O 2 525 kg / h 3288 m ³ N / h 28.07

HCI 1179kg / h 719m ³ N / h 6.14

InnertGase 10170kg / h 7705m ³ N / h 65.79

Hydrochloric acid should be prepared in 2 variants of the concentration, depending on the cooling conditions for the multistage isothermal absorption process:

Summer mode variant I t = 30 ° C c = 26% HCI

Winter operation variant Il t = 2O ⁰ C c = 29% HCI

c = mass fraction

The exhaust gas must be dewatered before absorption, in variant I by 1501 kg H ₂ O / h, in variant II by 2288 kg H ₂ CVh. Depending on the storage conditions, different amounts of dust enter the scrubbing tower with the exhaust gas, although the dust composition is constant: MgCl ₂ 67.85% C:

MgO 12,92% C:

H ₂ O 19.22% C:

Dust levels within a production cycle between downtime for cleaning and maintenance are approximately as follows:

a) after standstill 310kg / h

b) middle production cycle 403 kg / h

c) End production cycle 550 kg / h

To cope with the relatively extreme dewatering tasks, 90% of the total non-sulfated noble brine content of the composition is required for the overall process

MgCl ₂ 31.0% C:

MgSO ₄ 2.5% C:

H ₂ O 66.5% C:

introduced into the wash tower.

It is in the order of the dust accumulation (thus the decreasing MgO yield in the MgO process itself), the amounts of nichtentsulfatisierter noble brine as follows 0.63 t / h, 6.90 t / h and 7.25 t / h. In this order, the following wash tower solutions are obtained for the two types of drainage, the data being given in% by mass:

Variant I variants a) 8847kg / h, t = 78 ° C 9854 kg / h, t = 75 ^° C. MgCl ₂ 26.69% 23.97% _MgSO4 1.88% 1.68% H ₂ O 67.70% 68.77% HCI 3.73% 5.58%

Variant I variants b) 9159 kg / h, t = 82 ⁰ C 10146 kg / h, t = 76 ⁰ C MgCl ₂ 27.73% 25.03% _MgSO4 1.89% 1.70% H ₂ O 67.55% 68.73% HCI 2.84% 4.53% c) 9 632 kg / h, t = 85 "C 10619kg / h, t = 78 ° C MgCl ₂ 28.96% 26.26% _MgSO4 1.88% 1.70% H ₂ O 67.09% 68.26% HCI 2.07% 3.78%

These wash tower solutions formed as overflow are neutralized as described in the invention, mixed with the remaining portion of the required non-desulfated noble oil and almost completely desulfated. In addition, additional amounts of noble nails are brought to the desulphation and used for other purposes, otherwise an excess of CaCl ₂ is formed, unless you can use enough MgO-containing approaches with for neutralization. By increasing the amount of solution to be desulphated beyond the need in the actual MgO process, the degree of utilization of heat increases, while cooling water is saved at the same time.

Claims (7)

claims: 1. A process for the complex use of energy and recyclables from the exhaust gases of the thermal MgCl ₂ cleavage, wherein the cleavage takes place by direct contact of the MgCl ₂ solution with hot gases, the exhaust gases prior to introduction into the hydrogen chloride absorption stage of a mechanical dedusting with simultaneous exhaust gas cooling be subjected to a scrubbing tower and the cooling of the circulation solution of the scrubbing tower by means of external heat exchangers, characterized in that the scrubbing tower as additional washing liquid such a subset of cold, MgSO ₄ -containing fresh solution for the cleavage process in the form of so-called MgCl ₂ -Edelsole is supplied so that a sufficient dewatering of the exhaust gas for the production of highly concentrated hydrochloric acid is achieved in the downstream hydrogen chloride absorption stage, the supply of the other subset of required for the cleavage process fresh solution for the purpose of heating over part of the a oßenliegenden heat exchanger takes place as a coolant, and the solution discharged from the wash cycle of the scrubbing tower solution is neutralized with limestone, a part or the total amount of this neutralized still hot scrubbing solution with the guided over the external heat exchanger fresh solution for desulphation of the entire fresh solution mixed, and then the entire hot, desulphated solution is subjected to a hot-clarification process to separate the precipitated CaSO ₄ . 2. The method according to claim 1, characterized in that the hydrochloric acid produced in the hydrogen chloride absorption stage has at least 24% by mass of hydrogen chloride. 3. The method according to claim 1 and 2, characterized in that the subset of cold, MgSO ₄ -containing fresh solution which is supplied to the scrubbing tower ausn.acht 50 to 95% of the total solution required for the cleavage process. 4. The method according to claim 1 to 3, characterized in that the required CaCl ₂ amount and thus the required amount of HCl in the washing solution for desulfating the fresh solution by the operation of the scrubbing tower, by varying the fresh solution amount to be fed into the scrubbing tower and through the The degree of cooling of the circulation solution is adjusted. 5. The method according to claim 1 to 3, characterized in that the neutralization of the wash tower solution to be scrapped takes place in such a way that a small amount of guided over the outer heat exchanger and thus heated fresh solution provided with the required amount of ground limestone for neutralization, and this suspension then mixed with the main stream. 6. The method according to claim 1 to 3, characterized in that for neutralization in addition to limestone and MgO and MgCl ₂ -containing crushed approaches from the reactors of the thermal MgCl ₂ cleavage can be used. 7. The method according to claim 1 and 2, characterized in that the total amount of Frischi jsung, which supplied on the one hand to the scrubbing tower and on the other hand passed over the outer heat exchanger over the needs of the upstream splitting process is also eröht.