IL137512A

IL137512A - Method and apparatus for production of hydrogen chloride

Info

Publication number: IL137512A
Application number: IL13751200A
Authority: IL
Original assignee: Russian Nat Aluminium And Magn; Aluminium Alloies & Metallurg
Priority date: 1999-07-29
Filing date: 2000-07-25
Publication date: 2004-12-15
Also published as: AU4885400A; RU2173296C2; AU773791B2; IL137512A0

Description

METHOD AND APPARATUS FOR PRODUCTION OF HYDROGEN CHLORIDE RUSSIAN NATIONAL ALUMINIUM AND MAGNESIUM INSTITUTE & ALUMINIUM ALLOIES & METALLURGICAL PROCESSES LIMITED C: 39176 METHOD AND APPARATUS FOR PRODUCTTON OF HYDROGEN CHLORIDE FIELD OF THE INVENTION The present invention relates in general to the production of hydrogen chloride, and in particular to a method and an apparatus for the production of hydrogen chloride from chlorine-containing gases.

Description of the Prior Art A chlorine-containing gas or so called "anodic chlorine" is formed during the production of magnesium metal by electrolysis. This gas having the chlorine content of about 70-75 percent can be used in the form of hydrogen chloride for suppression of the hydrolysis of magnesium chloride during the dehydration of carnallite in fluidized bed dryers .

Flue gases generated in the fluidized bed dryers typically have the temperature of about 400-500° C and contain 0.5-6.0 percent of hydrogen chloride.

A method of burning chlorine accompanied by the production of artificial hydrogen chloride is also known in the prior art. This method is carried out by supplying a chlorine-containing gas and water vapor to the flame of a burning gas or liquid fuel. (see M.I. Levinsky et. al. "Hydrogen Chloride and Hydrochloric Acid", Overview Information, "Chemistry" Publishing House, . Moscow, 1985).

In this case the following equilibrium occurs: H20 + C12¾»2HC1 + 0.502 + 20.8 kcal The thermodynamic calculations of the reaction have shown that the balanced composition of the components in the reaction depends on the temperature and content of oxygen and water vapor in the gaseous phase. In order to shift the equilibrium in the direction of the formation of hydrogen chloride the following conditions are necessary: a high temperature (not lower than 1500° C) ; excess water vapor; and a minimum quantity of oxygen.

In the prior art, after burning of the chlorine-containing gas, the combustion products are cooled by various methods. Water, air or hydrochloric acid liquor are typically utilized as cooling agents. These methods are accompanied by quenching of the combustion products ( see J.G. Hornath and J. 0. S. MacDonald, "Process Technology International' January, 1973, page 61) .

There are also known methods of high-temperature burning utilized by the companies producing chlorine-containing organic products. Such high-temperature burning occurs during the processing of chlorine-organic waste by transforming such waste into a gas containing hydrogen chloride (see V.I. Abramova et. al. "Processing, Use and Destruction of Waste in the Production of Chlorine-Containing Organic Products", Overview Information, Series "Chlorine Industry", Moscow, 1977) .

The dioxins are not typically formed during the burning of chlorine-containing organic products and chlorine at the temperature exceeding 1400° C. It is also known that formation of dioxins occurs in the temperature range of 600-750° C. The dioxin formation occurs upon incomplete combustion of a fuel accompanied by the presence of carbon in the combustion products and during the slow cooling of such products. To prevent this occurrence and to achieve the most complete transformation of chlorine into hydrogen chloride, expeditious cooling down of the flue gases to the temperature range of about 400-500° C is necessary.

The known from the prior art process by Rhone-Poulenc includes the following steps: burning of chlorine organic products (COP) in a cyclone-type furnace at the temperature of 1200° C water cooling of the combustion products in a graphite heat exchanger; absorption of the cooled combustion products by a hydrochloric acid solution; and distillation.

In Japan, USA and Western Europe the process developed by Nittetu Chemical Engineering Ltd. (Tokyo) has also been utilized. The typical steps of this process are as follows: high temperature burning of the chlorine organic waste in a cyclone-type furnace; quenching of the combustion products with hydrochloric acid liquor in an immersion cooling device; hydrolysis; and subsequent distillation by extraction. A furnace which is used for burning of the chlorine organic waste generally includes a body, a burner, a combustion chamber and a gas outlet.

One of the main drawbacks of the above mentioned processes is utilization of water and hydrochloric acid liquors as cooling agents. This inevitably leads to a considerable increase of the water vapor content in the gaseous phase. It is known that such increase in water vapor content is unacceptable for the gaseous mixtures utilized in the fluidized bed dryers. Moreover, the degree of hydrogen chloride conversion is incomplete as the process achieves only about 95-96 percent conversion.

Summary of the Invention One of the major objects of the invention is to produce the mixture of hydrogen chloride and air having a predetermined composition. Another object of the invention is to exclude dioxins from this mixture and to provide a high degree of hydrogen chloride conversion.

The method of the invention consists of the following main steps: (a) burning of chlorine-containing gas in the flame of fuel combustion at the temperature of at least 1400° C in the presence of water vapor; and (b) cooling of the combustion products to the temperature of about 400-500° C by providing a direct contact of such products with a cooling gas or secondary air passing through the channels formed in the refractory lining wall of the furnace.

The apparatus of the invention consists of two chambers positioned within an interior portion of the furnace and having different temperature. In a combustion chamber the temperature is about 1400-1800° C, whereas in a chamber provided for cooling and quenching of a combustion product, the temperature range is between 400 and 500° C. The essential temperature drop between the chambers is the result of cooling of the combustion products or flue gases with a cooling gas or secondary air. In order to efficiently carry out this step, the quantity of the secondary cooling air in the furnace should be 2-5 times greater than the quantity of the flue gases.

The cooling secondary air in the form of specifically directed streams is delivered through the channels formed in the refractory lining wall of the furnace to the operational zone thereof. In this manner, a turbulent gaseous screen is developed within the operational zone by mixing the cooling secondary air with the flue gases. The cooling secondary air is substantially prevented from penetration into the combustion chamber. The turbulent gaseous screen produces fast cooling and hardening or quenching of the combustion products to the temperature range of 400-500° C. The dioxins are not formed at this temperature even if chlorine and carbon are present in the gaseous atmosphere of the operational zone including the combustion chamber. It should be noted, however, that the presence of chlorine and carbon in the gaseous mixture of the combustion chamber is unlikely during the normal operation of the burner and while the combustion temperature is in the range of 1400-1800° C.

The fast quenching of the combustion products drastically slows down the interaction of oxygen with hydrogen chloride in accordance with the following the reversible reaction: The above features of the invention provide high degree of hydrogen chloride conversion and exclude the formation of dioxins in the quantities which are ecologically dangerous.

BRIEF DESCRIPTION OF THE DRAWINGS Other advantages and features of the invention are described with reference to exemplary embodiments, which are intended to explain and not to limit the invention, and are illustrated in the drawings in which: Fig. 1 is a longitudinal cross-sectional view of an apparatus of the invention; and Fig. 2 is a cross-sectional view according to section line 2-2 of Fig. 1.

Description of the Preferred Embodiment Referring now to Figs.l and 2 showing an apparatus or a furnace 10 for the production of hydrogen chloride in which the process of the invention is carried out by burning chlorine-containing gases in a flame of carbon-hydrogen fuel in the presence of hydrogen-containing materials. The apparatus 10 includes an outer housing or shell 1 with an interior area or operational zone 11 extending along a longitudinal axis thereof A-A. A product outlet 8 is situated at a front end of the operational zone. A refractory lining 2 is provided between the operational zone 11 and outer housing 1 in such a manner that a substantially hollow space 14 is developed therebetween. A plurality of channels 6 passing through the refractory lining 2 are formed to provide communication between the substantially hollow space 14 and the operational zone 11.

The channels 6 are distributed along the periphery of the refractory lining 2 and are located substantially with one plane extending generally perpendicular to the longitudinal axis A-A and/or to the direction of flow of the combustion products within the operational zone..

As illustrated in Figure 1, each channel 6 is inclined toward the product outlet 8 and is positioned at an angle of about 60°- 90° to the inner surface 15 of the refractor lining, to the longitudinal axis A-A and/or to the direction of flow of combustion products within the operational zone.

Figure 2 shows that each channel 6 is also interposed an angle ft of about 30° to respective transverse axes Bi-Bj,* B2 - B2 B3 - B3/ etc. Thus, a stream of cooling secondary air exiting each channel 6 into the operational zone 11 is directed tangentially to the inner surface 15 of the refractory lining.

The plane of the channels 6 separates the operational zone 11 into a combustion chamber 4 which extends toward a base wall 12 of the refractory lining and a cooling chamber 5 extending in the direction of the product outlet 8. A burner 3 supported by the base wall 12 is provided at the combustion chamber 4.

The motion of the gaseous streams within the operational zone 11 in the direction of the outlet 8 is facilitated by a low pressure area developed within the cooling chamber 5.

In operation, the cooling gas or secondary air is delivered to the substantially hollow space 14 by means of inlets 1 which are distributed along the periphery of the outer housing. Upon exiting the channels 6 into the operational zone 11, the cooling secondary air forms a turbulent gaseous screen in the area between the combustion chamber 4 and the cooling chamber 5. The following elements of the geometry of the channels 6 substantially contribute to the formation of the turbulent gaseous screen: (a) Due to the angle ft the streams of cooling gas enter the operational zone in the direction tangential to the inner surface 15 of the refractory lining. As illustrated in Fig.2, this adds a rotational component to the movement of the cooling gas within the operational zone; and (b) Due to the angleOt the streams of cooling gas are directed linearly toward the product outlet 8 at an angle between 60° and 90° to the direction of flow of the combustion products or flue gases generated by the burner 3.

In the operation of the invention, it is essential to ensure a unidirectional flow of the cooling secondary air toward the product outlet 8. This is necessary to prevent penetration of the low temperature cooling gas into the high temperature region of the combustion chamber 4. Such unidirectional movement of the cooling gas flow, among other factors, is the result of the geometry of the channels 6 and the lower pressure area formed within the cooling chamber 5. Furthermore, to exclude extension of the cooling gas into the combustion chamber 4, the speed of its movement within the channels 6 should be relatively high or approximately between 8 and 20 nm/sec.

According to the method of the invention, a mixture of hydro-carbon fuel, air, chlorine-containing gas and hydrogen -containing product (water vapor, for example) are supplied into the operational zone 11 by means of the burner 3. In the combustion chamber 4 a reaction between the chlorine-containing gas and the hydrogen-containing product occurs resulting in the formation of a hydrogen chloride containing gas mixture. The temperature of the mixture is in the range of 1400 to 1800° C. The combustion products in the course of delivery from the combustion chamber 4 to the cooling chamber 5, pass through or collide with the high turbulence screen of the cooling secondary air having the temperature of approximately 10-60° C. The combustion products are ejected, efficiently mixed with the secondary air and expeditiously cooled down to the temperature of about 400°-500° C. Then, the combustion products are evacuated from the furnace 10 through the product outlet 8 situated at the front end of the apparatus .

Among the essential steps of the method of the invention are: (a) burning of chlorine containing gas in the flame of fuel combustion at the temperature of at least 1400° C in the presence of water vapor; and (b) cooling of the combustion products to the temperature of about 400-500° C by providing a direct contact of these products with the cooling secondary air forming the turbulent gaseous screen.

The temperature in the combustion chamber 4 is about 1400-1800° C, whereas in the cooling chamber 5 the temperature is between 400° and 500° C. The essential temperature drop between the chambers 4 and 5 is the result of cooling of the combustion products or flue gases formed in the combustion chamber by the cooling secondary air. In order to efficiently carry out this step, the quantity of secondary air in the furnace should be 2-5 times greater than the quantity of the flue gases.

The turbulent screen formed by mixing of the cooling secondary air and the flue gases produces fast cooling and/ or quenching of the combustion products to the temperature range of 400-500° C. The dioxins are not formed at this temperature even if chlorine and carbon are present in the gaseous atmosphere of the operational zone 11 including the combustion chamber. The presence of chlorine and carbon in the gaseous mixture of the combustion chamber 4 is unlikely during the normal operation of the burner 3 and while the temperature in the combustion chamber 4 is approximately 1400-1800° C.

The method and apparatus of the invention were tested in the laboratory conditions. Examples of the method of the invention are presented hereinbelow: Example 1: A conventional furnace having substantially cylindrical configuration and operating at a temperature of about 1600° C was used for burning of chlorine-containing gas. Cold secondary air was supplied to the interior of the furnace through a single cooling outlet provided at its side wall . The combustion products generated by the burner entered the combustion chamber at the temperature of about 1600° C. These products were mixed with the secondary air exiting the outlet and having the temperature of approximately 18° C.

As a result, the gas-air mixture of required composition having the temperature of about 400-500° C was formed. The temperature of the gases after the cooling outlet supplying the secondary air and before the product outlet of the furnace decreased from 1600° C to about 400 -550° C. The degree of hydrogen chloride conversion achieved was approximately 90 percent.

Example 2 : In this instance, similar to Example 1, the burning of chlorine-containing gas was carried out at the temperature of about 1600° C in the conventional substantially cylindrical furnace.

To provide a supply of a cooling secondary air, a plurality of channels was formed within refractory lining wall of the furnace in the manner discussed with reference to Figures 1 and 2. The temperature of the gaseous mixture in the combustion chamber was about 1600° C, whereas the temperature in the cooling chamber was in the 400-500° C range. The temperature of the cooling secondary air exiting the plurality of channels was about 18° C. The entire drop of the temperature of the gaseous mixture between the combustion and cooling chambers occurred in the region adjacent the channels supplying the cooling secondary air.

The resulted degree of hydrogen chloride conversion in this Example was approximately 99.3 percent.

As discussed hereinabove, the invention enables a user to efficiently utilize the chlorine containing gas or "anodic chlorine" which is typically generated during the production of magnesium metal by electrolysis. Specifically this gas in the form of hydrogen chloride is utilized during the dehydration of carnallite in the fluidized bed dryers. To facilitate this task, a gas-air mixture is produced containing 0.5-6.0 percent of hydrogen chloride and having the temperature in the range between 400 and 500° C. The content of dioxins in the flue gases is at an ecologically acceptable level.

The process of the invention is carried out by the presence of hydrogen containing material, such as water vapor, during the burning of a chlorine-containing gas in a flame of carbon-hydrogen fuel. The combustion products are expeditiously cooled down and quenched by mixing thereof with the secondary air. Such step is carried out upon passing the combustion products through the turbulent screen formed by the streams of cooling secondary air having the temperature between 10 and 50° C. These streams are delivered through the channels or nozzles formed in the inner refractory lining wall of the operational zone of the apparatus .

As described hereinabove, the method and apparatus of the invention enable a user to produce a gaseous mixture having a predetermined composition and temperature, which mixture after being utilized as a flue gas in the fluidized bed dryers achieves a high degree of hydrogen chloride conversion.

Claims

137512/2 - 13 - ΤΉΕ CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

1. A method of production of hydrogen chloride from chlorine-containing gases, the method consisting of the following steps: (a) burning of chlorixie-contaiiung gases in a flame of hydrogen-carbon fuel in the presence of hydrogen-containing materials so as to produce combustion products; and (b) cooling of said combustion products by passing thereof through a turbulent screen of a cooling gas having a temperature substantially lower than a temperature of said combustion products.

2. The method according to claim 1, wherein said cooling gas is cooling air and said hydrogen-containing materials are water vapor.

3. The method according to claim 1 or claim 2, wherein said step of burning is carried out at a temperature of about 1400-1800° C and said combustion products are cooled to a temperature of about 400-500° C.

4. The method according to any one of claims 1 to 3, wherein said cooling air is in a form of a turbulent gaseous screen positioned in a plane substantially perpendicular to the direction of movement of the combustion products.

5. The method according to claim 4, wherein said turbulent gaseous screen is situated between an area of said burning of the cUorine-containing gases and an area of said cooling of the combustion products.

6. An apparatus for production of hydrogen chloride by burning chlorine containing-gases in a flame of carbon-hydrogen fuel in the presence of hydrogen-contaimng materials, the apparatus consisting of: an outer housing and an interior area forming an operational zone extending longitudinally between a base wall and a product outlet, a refractory lining situated 137512/2 - 14 -between said operational zone and outer housing so as to form a substantially hollow- space therebetween, wherein a plurality of channels extending throughout said refractory lining are formed to provide communication between said substantially hollow space and said operational zone, said channels being oriented tangentially to an inner surface of said refractory lining and forming an acute angle with the direction of flow of combustion products produced in the operational zone, said channels separating the operational zone into a combustion chamber in the vicinity of the base wall and a cooling chamber in the vicinity of the product outlet.

7. The apparatus according to claim 6, further comprising a burner being in communication with said combustion chamber and situated at said base wall, and a cooling gas being delivered through said channels so as to form a turbulent gaseous screen in an area between the combustion and cooling chambers.

8. The apparatus according to claim 6 or claim 7, wherein said apparatus is a furnace for production of hydrogen chloride and a longitudinal axis of each said channel extends at an angle between 60° and 90° to the direction of flow of combustion products within the operational zone.

9. The apparatus according to any one of claims 6 to 8, wherein said plurality of channels are positioned within a plane positioned substantially perpendicular to a longitudinal axis of the operational zone or the direction of flow of the combustion products.

10. The apparatus of claim 9, wherein said cooling gas is cooling air, and to substantially prevent penetration of said cooling air into the combustion chamber a rate of flow of said air in said channels is between 8 and 20 nm/sec. 137512/2 - 15 -

11. A method of production of hydrogen chloride from chlorine-containing gases substantially as herein described with reference to any one of the embodiments of the invention illustrated in the accompanying drawings and/or examples.

12. Hydrogen chloride when produced by a method according to any one of claims 1 to 5 or 11.

13. An apparatus for production of hydrogen chloride substantially as herein described with reference to any one of the embodiments of the invention illustrated in the accompanying drawings and/or examples.