JP2012046817A - Acid cleaning agent for cargo tank or the like of chemical tanker and automatic acid cleaning method of the cargo tank or the like - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an acid cleaning method in which acid cleaning is performed automatically in an unmanned manner by using a tank cleaning device in place of a manual acid cleaning method having problems from the viewpoint of safety and efficiency, in acid cleaning work of a stainless cargo tank of a chemical tanker; and to provide an acid cleaning agent which is suitable for the automatic acid cleaning method and capable of obtaining high cleaning effect.SOLUTION: The acid cleaning agent has a constitution including nitric acid, hydrofluoric acid, sulfuric acid, an organic acid, a polyvalent alcohol, a viscous aid, a complex compound, and a defoaming agent. In the automatic acid cleaning method of a stainless cargo tank of a chemical tanker, the acid cleaning agent and the tank cleaning device are used.

Description

Detailed Description of the Invention

  In the pickling of the inner surface of a stainless steel cargo tank, slop tank or the like of a chemical tanker, the present invention is used to wash the thermal oxide film, red rust, rust rust, and oils and fats generated on the surface of the stainless steel. The present invention relates to an automatic pickling method using an apparatus and a pickling agent suitable for use in this pickling method.

  The chemical tanker is used to load and transport a liquid chemical substance on a cargo tank in the ship. Since liquid chemical substances are diverse and often transport highly corrosive chemical substances, unlike ordinary oil transport tankers, chemical tanker cargo tanks have corrosion-resistant steel sheets, such as austenitic materials such as SUS304 and SUS316. Stainless steel is commonly used.

  In the construction of this chemical tanker, the inner surface of the stainless steel cargo tank is removed from the welded portion during construction, the dirt generated during construction is cleaned and the stainless steel is passivated in the final construction process. Perform the washing process.

  When pickling the inner surface of a chemical tanker's cargo tank, an operator must bring an acid cleaner, spray pump, or other equipment into the tank and manually spray the acid cleaner over the entire wall in a mist. Is commonly done today. However, in recent years, cargo tanks have become larger and the ceiling height has reached 15 to 20 meters, so that pickling work by humans is increasingly poor and the work environment is poor, and toxic gas is caused by direct exposure to the acid cleaning agent atmosphere. It is dangerous because of oxygen deficiency and it places an excessive burden on workers.

  In addition, when the acid cleaning agent used is sprayed using a liquid acid cleaning agent, there is a problem that dripping occurs, pickling spots occur, and the oxide scale is left behind. In order to prevent this, an acid cleaning agent in which a mixed acid such as hydrofluoric acid is pasted is used, and after a pickling operation, a mechanical polishing operation is also used to remove the remaining scale. A stepped process is used. As described above, the acid cleaning process for the inner surface of the cargo tank of a chemical tanker is very inefficient, and has a drawback of requiring a great deal of labor in a highly dangerous and harsh working environment.

The present invention has been made in view of the actual situation, and in the pickling work method for the inner surface of a tank of a chemical tanker, it is an automatic that can be replaced with an efficient and safe work instead of the manual pickling method by a human. There has been a demand for the development of a suitable pickling agent when a tank cleaning apparatus (Non-patent Document 1, Patent Document 1, Patent Document 2) is used in the pickling method and the automatic pickling method.
Shipbuilding Design Handbook 4th edition, pages 739-741 Edited by Kansai Shipbuilding Association August 8, 1983 Published by Kaibundo Publishing Co., Ltd. Special table 2008-503337 JP 2008-290033 A

  As described above, an object of the present invention is to provide a method for solving the problems related to the pickling operation of the inner surface of a cargo tank of a chemical tanker. Commercially available tanks described in Non-Patent Document 1, Patent Document 1, Patent Document 2, and the like described above, using a pasty acid cleaning agent of hydrofluoric acid, which has been conventionally used in pickling operations that have been performed manually When the acid cleaning operation is carried out under normal cleaning conditions using a cleaning device, it is difficult to uniformly apply the acid cleaning agent to the inner wall surface of the tank. It is difficult to remove completely.

  For this purpose, when using the optimum pickling detergent in the automatic pickling method, consider optimization of cleaning conditions such as discharge speed, pressure and discharge liquid volume that match the performance of the tank cleaning device, and tank cleaning device As a result, it becomes a problem to develop an acid cleaning agent suitable for a tank cleaning apparatus that can obtain an optimal adhesion state of the tank wall surface, does not cause dripping and pickling spots, and can completely remove oxide scale. By solving this problem, it is possible to establish automation of a tank pickling operation for a chemical tanker using a tank cleaning apparatus.

  By using the automatic pickling work of the present invention and the pickling agent most suitable for this work, it is free from manual pickling work that requires a lot of labor in the cargo tank of a chemical tanker, and is safe and efficient. Can be pickled. Furthermore, if the pickling operation can be standardized by automation, uniform and stable pickling treatment is guaranteed without being affected by the experience, judgment, and skill level of the operator.

Hereinafter, embodiments of the present invention will be described in more detail with reference to the drawings.
FIG. 1 is a schematic configuration diagram schematically showing a cargo tank pickling facility for a chemical tanker used in the present invention.

  The tank cleaning device (4, 5) used in the present invention is a cleaning device that cleans the inside of the tank by injecting a cleaning liquid toward the inner wall of the cargo tank (1), and an acid cleaning agent installed on the upper deck. A storage tank (2) for storage, an acid cleaning agent supply step comprising a supply pump (3), and a spray nozzle (5) for cleaning the tank inner surface using the acid cleaning agent supplied from the storage tank (2) A tank automatic cleaning device equipped with a cleaning process having a swirling cylinder (4) and a chemical recovery process for recovering the acid cleaning agent after pickling through the suction pump (6) and reusing it is used.

  In the pickling method using a normal tank cleaning device, a predetermined amount of the acid cleaning agent is put in the storage tank (2) in advance and is flowed and pressurized through the supply pump (3) and sent to the swivel cylinder (4). While the swivel cylinder (4) rotates 360 degrees around the Y axis, the spray nozzle (5) at the tip connected to the swivel cylinder (4) spouts cleaning liquid while rotating 360 degrees relative to the X axis, and the tank wall surface (1) The acid cleaning is started by applying an acid cleaning agent to the surface. One cycle can be completed in 3 to 15 minutes while the swivel cylinder (4) rotates 360 degrees around the Y axis, and the acid cleaning is completed by repeating this cycle 4 to 20 times in succession. I found out that I could do it.

  When the acid cleaning is started, the cleaning liquid ejected from the spray nozzle (5) collides with the wall surface of the cargo tank (1), and part of the cleaning liquid flows down to the bottom of the tank along the wall surface. Since the bottom of the tank is designed with an inclination, the liquid flows down naturally and flows into the suction pit portion (7) of the cargo tank. In order to circulate and reuse the liquid, the suction pump (6) installed in the vicinity of the suction pit (7) is sucked up and introduced into the acid cleaning agent storage tank (2) installed on the upper deck. This tank discharge valve (not shown) is connected to the suction part of the pump, the discharge side of the pump is connected to a filter (not shown), and the clarified liquid by filtration is supplied to the tank cleaning process. The acid cleaning agent is recycled and reused.

  When the acid cleaning is completed for a predetermined time or a predetermined cycle, the liquid accumulated in the bottom of the tank is quickly recovered in the upper deck tank. The time from the end of the pickling to the transition to the water washing process corresponds to the reaction time of the acid cleaning agent and is an important factor for determining the quality of the pickling finish. 30 to 60 minutes from the end of the pickling, preferably 20 to A surface reaction time of 40 minutes is taken. The supply of water (8) is transferred to a water washing step of supplying water to the tank cleaning devices (4, 5) via the three-way automatic valve (9) and cleaning the interior of the cargo tank (1). When the time for shifting from the pickling process to the water washing process is delayed, there is a concern that a drip trace or pickling spots of the acid cleaning agent may occur. In the water washing step, it was found that the rotating cycle of the swivel cylinder (4) was operated for 4 to 12 cycles, preferably 6 to 8 cycles, and was terminated by spraying water.

  Next, the cleaning waste liquid treatment of the cargo tank (1) is performed by operating the suction pump (6) from the waste water outlet (11) to the storage tank of the waste water treatment ship via the three-way automatic valve (10).

  As a result of examining the optimum acid cleaning agent in the automatic cleaning method performed using the tank cleaning device described above, the optimum acid cleaning agent is nitric acid, hydrofluoric acid, sulfuric acid, organic acid, polyhydric alcohol, It was found to have a constitution containing a viscosity aid, a complex compound, and an antifoaming agent. Each component other than hydrofluoric acid and sulfuric acid, which are usually used as acid detergents, had the following blending purpose and action. The acid cleaning agent produced by this component structure has made it possible to provide an acid cleaning agent that can be used in an automatic pickling method that is suitable for a tank cleaning apparatus.

  The organic acid contained had an effect of controlling the pickling speed, and the complex compound had an effect of promoting gloss on the inner wall surface of the tank. In addition, when spraying the acid cleaning agent from the nozzle, an appropriate viscosity is required to retain the acid cleaning agent that has reached the tank wall surface. It was effective in making the adhesion state of the tank wall of the agent good. When spraying with a pasty acid detergent with high viscosity and mixed acid with hydrofluoric acid, a fine spray state of the acid detergent cannot be obtained and it becomes difficult to uniformly apply to the tank wall surface. As a result, dripping and pickling spots occurred, and a good pickling effect was not obtained. In addition, liquid acid cleaning agents that are not mixed with hydrofluoric acid and have no viscosity are dripping drastically, and the contact reaction time between the acid cleaning agent and the stainless steel on the tank wall surface is not sufficient, resulting in good pickling effect I can't get it. For this reason, it has been found that an acid cleaning agent having a slight and moderate viscosity is optimal, and the blending of an organic acid and a viscosity aid controls this viscosity.

  The antifoaming agent contained is sprayed with acid cleaning agent in the air until the acid cleaning agent jets from the nozzle head of the tank cleaning device and reaches the tank wall 10 to 20 meters ahead. In order to avoid danger and to prevent foam generation on the surface of the acid cleaning agent applied to the tank wall surface, it is included in the acid cleaning agent in advance. As a result, the effect of being suppressed was obtained.

  Also, since the main component of the acid cleaner is volatile, the nitric acid is volatile. When it reaches the wall surface of the cargo tank, it evaporates from the stainless steel surface and dries quickly. The liquid pressure of 1 to 1.2 MPa was required, but the evaporation rate of hydrofluoric acid was controlled by blending an antifoaming agent and a polyhydric alcohol to make the cycle of the swirl cylinder longer by 15 to 20 minutes. It became possible to respond even with a cycle. This means that a low operating pressure of 0.4 to 0.6 MPa can be achieved instead of operating the system pressure in the cleaning process at 1 to 1.2 MPa, and the supply pump specification becomes a general-purpose product specification and is inexpensive. Moreover, it leads to a power saving effect. In particular, the allowance for the transition time to the water washing step after the end of pickling can take a long time for recovering the liquid after the end of pickling, which can be beneficial for the recovery of the liquid that has been circulated. all right. Furthermore, in the summer, the temperature inside the cargo tank is exposed to extremely high temperatures, so that the acid cleaning agent evaporates instantly, increasing the risk of occurrence of smut and pickling spots. It was found that these concerns can be resolved by blending an appropriate amount of alcohol.

It is the schematic block diagram which showed typically the cargo tank pickling equipment of the chemical tanker used by this invention.

DESCRIPTION OF SYMBOLS 1 Cargo tank 2 Acid cleaning agent storage tank 3 Acid cleaning agent supply pump 4 Washing machine swivel cylinder 5 Washing machine spray nozzle 6 Suction pump 7 Pit 8 Water 9 Three-way automatic valve 10 Three-way automatic valve 11 Washing waste water outlet

Claims (4)

  An acid cleaning agent comprising nitric acid, hydrofluoric acid, sulfuric acid, an organic acid, a polyhydric alcohol, a viscosity auxiliary agent, a complex compound, and an antifoaming agent.   The organic acid is composed of one or more of oxalic acid, citric acid, and tartaric acid, the polyhydric alcohol is composed of ethylene glycol or glycerin, and the viscosity aid is polyacrylamide, carboxymethylcellulose, or polyvinyl alcohol. The complex compound is composed of at least one of ethylenediaminetetraacetic acid, hydroxyethylethylenediaminetriacetic acid and diethylenetriaminepentaacetic acid, and the antifoaming agent is an emulsion antifoaming agent. The acid cleaning agent according to claim 1.   The nitric acid is 10 to 20%, preferably 15 to 20%, the hydrofluoric acid is 2 to 10%, preferably 3 to 8%, the sulfuric acid is 3 to 15%, preferably 5 to 10%, and the organic acid is 2 to 10%, the polyhydric alcohol is 1 to 10%, preferably 3 to 6%, the viscosity auxiliary agent is 10 to 20%, the complex compound is 1 to 5%, and the antifoaming agent is 0.1 to 10%. The acid cleaning agent according to claim 1 or 2, comprising 0.25%.   When pickling a stainless steel cargo tank of a chemical tanker, the acid cleaning agent according to any one of claims 1 to 3 is used, and automatic acid cleaning is performed using a commercially available tank cleaning device. Pickling method.

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