CS258843B1 - A method for deactivating pyrophoric substances in coke oven purification plants - Google Patents

Abstract

The invention solves a method of effective deactivation of pyrophoric sulfides present in devices for processing and cleaning industrial gases, especially benzene scrubbers in metallurgical and mining coke ovens in which bentol is scrubbed from coke oven gas with scrubber oil. The scrubber is steamed with water vapor at a temperature of min. 200 °C and a pressure of 0.2 to 2.0 MPa until the analysis of the vapors leaving the scrubber and cooled to a temperature of 25 to 35 °C shows the composition: oxygen ... min. 18 vol. % hydrogen ... max. 0.1% vol. methane ... max · 0.1% vol. higher homologues of benzene ... max. 20 mg.m-2 carbon monoxide ... max. 0.1% vol. carbon dioxide ... max. 0.1% vol. sulfur dioxide ..· less than 5 ppm and the temperature of any place in the washing machine 24 hours after the end of steaming is less than 29 °C. The description of the invention is supplemented by one example of a practical embodiment.

Description

The present invention provides a method for effectively deactivating pyrophoric sulfides present in industrial gas treatment and purification plants, in particular benzene scrubbers, in metallurgical and mine coking plants, in which benzene is washed out of coke oven gas by scrubbing oil.

The tar and ammonia-free coke oven gas and cooled in the end coolers are fed to scrubbers where benzene hydrocarbons are scrubbed with scrubbing oil. These benzene scrubbers are cylindrical containers with a diameter of about 5 and a height of about 24 meters, which are divided in height over several floors, sections on which the filling, formerly hazel, is placed, Raschig, Bialecka or Pall-rings or metal spirals. The filler has a large surface area per volume unit and ensures perfect contact of the gas with the liquid and thus absorption of benzene by the wash oil. Benzol scrubbers are sprinkled with washing oil from above, and the gas is fed to the bottom of the scrubbers. In addition, some benzene scrubbers have internal scrubbing oil recirculation and are typically connected in series with two or three scrubbers. The purpose of the operation is to first absorb the benzene present in the gas into the scrubbing oil and then absorb the benzol from the saturated scrubbing oil with heat and steam. Long-term operation of benzene scrubbers results in the formation of solid or semi-solid deposits due to corrosion, polymerization and polycondensation of the substances present, which impart increased hydrodynamic resistance to gas passage. If this resistance rises above the technologically acceptable limit, the washing machine load must be removed and replaced, as steam steaming or washing with hot washing oil or ammonia water is no longer effective. In practice, this means that the washing machine must be blinded and steamed at a pressure of 4 bar and a temperature of about 130 ° C until all volatile components present on the filler and the walls of the washing machine have evaporated. However, even after more than six months of vaporization and subsequent opening of the manhole and atmospheric oxygen ingress into the interior of the washing machine, a strongly exothermic reaction occurs at various locations in the washing machine and becomes so hot that the exterior coating of the washing machine is rendered uncoated. Therefore, the opening must close immediately and restart steaming, which takes a few more months. Production losses are increasing and substitute operation is not possible, as experience shows that the washing machines will last many years and therefore no spare facilities are built for them.

The immediate cause of these exothermic reactions is the presence of hydrogen sulphide, water vapor and oxygen, which, together with higher temperatures, result in corrosion, often intercrystalline, even in very high-grade steels and pyrophoric sulfides. These sulfides have a submicroscopic dimension usually in the range of 1 to 100 nm and are catalytically active formed mostly by the reaction of metal oxides with hydrogen sulfide or sulfur compounds in the presence of water vapor and oxygen. If the oxygen content rises above a certain threshold, for example when the scrubber is opened, the oxidation of the sulfides proceeds spontaneously, accompanied by a large amount of heat generation and local temperatures usually above the ignition temperatures of the flammable gas or vapor components present. If an explosive gas-oxygen mixture is present in an area where active metal sulfides are present, it is very likely that the mixture and the explosion will ignite within a short time. Considering that even long-term steaming of 0.45 MPa steam does not inactivate pyrophoric sulphides and is therefore ineffective, other proposals have been made to replace the load by flooding the machine with water and gradually reducing its level in the machine while removing the load in layers. permanent sprinkling. However, this method is speculative because the pressure of the water charge on the bottom and walls of the corrosion-weakened washing machine could lead to its destruction. An alternative is the previously unexplored method of inerting the washing machine space with nitrogen gas, carbon dioxide or flue gas.

The above-mentioned problems and drawbacks are solved by a method of deactivating pyrophoric substances in coke oven gas cleaning plants, for example in benzol scrubbers in which benzol is absorbed by washing oil by steam steaming according to the invention. . 200 ° C and a pressure of 0.2 to 2.8 MPa until the analysis of the vapors leaving the machine and cooled to 25 to 35 ° C shows the composition:

oxygen hydrogen methane higher benzene homologues

min. 18 * obj. max. 0.1 % vol. max. 0.1 % vol. max. 20 mg.m ”3

carbon monoxide ... max. 0.1% by volume: carbon dioxide ... max. 0.1% by volume sulfur dioxide ... less 5 ppm and the temperature of any point in the washing machine 24 hours after the steaming is less than 28 ° C.

The advantage of the described method of deactivating pyrophoric substances in benzene scrubbers compared to the known methods consists mainly in a very significant shortening of the interval of this operation from more than seven months to seven weeks. In addition to the uncertain and risky results of previous steaming methods, this method, with absolute safety assurance, fulfills the rapid and perfect process of pyrophoric deactivation as well as the polymerization and polycondensation process, after which the old washing machine filler can be gradually removed.

The following practical example illustrates the nature of the process according to the invention and the sequence of individual operations carried out in this process.

After 21 years of operation, the petrol scrubber was shut down by draining the scrubbing oil, and all gas and oil supplies were closed and the scrubber was disconnected from the outside. The condensate drain was opened and steam at a temperature of 130 ° C was admitted to the washer under a pressure of 0.45 MPa and an air tank opened. This low-pressure steam released scrubbing oil residue, which is initially entrained in large quantities with steam condensate. This steaming stage lasted 7 days and was sufficient to empty the scrubber from the wash oil, and then steam at 200 ° C and a pressure of 1.8 MPa was introduced into the foot of the scrubber. The vapors from the benzene scrubber were passed through an end cooler and after four weeks of steaming with high pressure steam had the following composition:

oxygen: · hydrogen:

methane:

benzene:

naphthalene:

higher homologues of benzene:

carbon monoxide:

carbon dioxide:

sulfur dioxide:

highest working temperature prostor benz. washing machines:

% vol.

»Obj.

less than 0.5% v / v -3 mg: m = 3 mg.m

420 mg.m less than 0,1% vol. Less than 0,1% vol.

ppm ° C

After the next week of steaming with high pressure steam, the fumes from the washing machine showed the following composition:

oxygen: 20,8 »Vol. hydrogen: less than 0,2% vol. methane: less than 0,2% vol. carbon monoxide: less than 0,1% vol. carbon dioxide: less than 0,1% vol. sulfur dioxide: 0 benzene: less than 10 mg.m ³ naphthalene: 24 mg.m ³

higher benzene homologs: 310 mg.m prostor benz. washing machines: 26 ° C

Over the next week, six weeks after the introduction of the steam into the benzol scrubber, its air composition was as follows:

oxygen:

hydrogen:

20,0 »Vol.

less than 0,2% vol.

methane: less than 0,2% vol. carbon monoxide: less than 0,1% vol. carbon dioxide: less than 0,1% vol. sulfur dioxide: 0 benzene: less than 10 mg.m ^-3 naphthalene: 9,5 mg.m

higher benzene homologs: 85 mg.m ^-J prostor benz. washing machines: 27 ° C

Seven weeks after the introduction of steam into the benzole scrubber, the concentration of higher homologues dropped below 20 mg.m ^-3 , the other components of the scrubber remained unchanged. Under this condition and the composition of the atmosphere in the machine, the steam supply stopped and the machine was cooled by opening the air tank and the upper hatch in the machine lid. Since the sulfur dioxide content was still below 5 ppm and the temperature inside the washing machine was not higher than 28 ° C, the side hatches of the top floor were uncoiled and the washing machine was rinsed, continuously checking the temperature inside the washing machine and the contents of the above components.

Claims (1)

SUBJECT OF THE INVENTION Process for deactivating pyrophoric substances in coke oven gas purification plants, for example in benzol scrubbers in which the absorption of benzol by washing oil is carried out by steam-steaming, characterized in that the scrubber is steam-steamed at a temperature of min. 200 ° C and a pressure of 0.2 to 2.0 MPa until the analysis of the vapors leaving the machine and cooled to 25 to 35 ° C shows the following composition: oxygen ... min. 18 »Art. hydrogen • .. max. 0,1% vol. methane • .. max. 0,1% vol. higher benzene homologues ... max. 20 mg.m ^-3 carbon monoxide • ·. max. 0,1 »vol. carbon dioxide ... max. 6,1 t vol. sulfur dioxide .. · less than 5 ppm and the temperature of any point in the washing machine 24 hours after the completion of steaming is less than 28 ° C.