JPH06123592A - Removing method for deposit on outer surface of heat transfer tube - Google Patents

Abstract

PURPOSE:To easily and completely remove deposit on an outer surface of a heat transfer tube for recovering heat of exhaust gas, etc. CONSTITUTION:Chemical cleanser 11 containing mixture of nonionic surface active agent and ammonium carbonate is sprayed on outer surfaces of heat transfer tubes 2, 3, 4 in which gases to be thermally recovered flow to dissolve fats and oils in deposits Then, waters are sealed in the tubes, the sealed waters are vibrated by an ultrasonic oscillator 21, the vibration is transmitted to outer surfaces of the tubes to react sulfuric acid with the cleanser to generate foaming operation in the deposits to cause the deposits to become porous to be embrittled. Then, the deposits are removed from the tubes by water rinsing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for removing deposits on the outer surface of a heat transfer tube, and more particularly to a heat transfer surface on the outer surface of a heat transfer tube of a device for recovering heat in exhaust gas from a main engine such as diesel or gas turbine. The present invention relates to a method suitable for removing deposits attached to the outer surface.

[0002]

2. Description of the Related Art In a marine diesel engine or a thermal power plant, exhaust heat of exhaust gas is recovered by an exhaust gas economizer or a heat exchange device for recovering exhaust heat in order to improve fuel efficiency. Soot of exhaust gas and dirt from adhered ash are generated on the outer surface of the.

Particularly, in an exhaust gas economizer for a marine diesel main engine, exhaust heat recovery is carried out up to an acid dew point exhaust gas range of 90 to 120 ° C. However, the deterioration of fuel and exhaust heat recovery in a temperature range below the acid dew point are performed. Therefore, in the low temperature heat recovery part of the exhaust gas economizer, unburned carbon, iron sulfate, vanadium oxide, etc., sulfuric acid generated by sulfur in the fuel, and dust that easily precipitates from impurities in the fuel due to this sulfuric acid In addition, it adheres to the low temperature heat recovery part below the acid dew point and causes problems such as an increase in draft loss and a decrease in exhaust heat recovery rate. For this reason, conventionally, the deposit adhered to the outer surface of the heat transfer tube in the low temperature heat recovery section of the exhaust gas economizer,
It is removed by the washing method.

FIG. 2 schematically shows this conventional washing method together with the structure of an exhaust gas economizer.
In FIG. 2, 1 is an exhaust gas economizer casing 1.
The preheater tube 2, the low-pressure evaporator tube 3 below the preheater tube 2, and the like are provided in the low-temperature heat recovery section above the inside thereof.
Further, a superheater pipe 4 is arranged in the lower part of the inside, and exhaust gas flows outside these pipes. Then, the washing water is sprayed from a large number of nozzles 7 provided above the preheater 2 of the washing pipe 6 to which the valve 5 is attached, and the low temperature heat recovery unit such as the preheater pipe 2 and the low pressure evaporator pipe 3 Are removed by washing and are stored in a waste liquid tank 10 through a cleaning waste liquid receiving gutter 8 and a discharge pipe 9 arranged below the superheater pipe 4 located in the lower part of the exhaust gas economizer casing 1.

[0005]

By the way, in the exhaust gas economizer, about 30 to 60% of the deposits in the low-temperature heat recovery section of the preheater pipe 2 and the low-pressure evaporator pipe 3 have imperfect water permeability. It is unburned carbon and soot which are products of combustion, and the other is ash mainly composed of SiO ₂ and Al ₂ O ₃ .
Further, the preheater pipe 2 and the low-pressure evaporator pipe 3 are provided with fins to improve recovery of exhaust heat, and the vertical arrangement of the pipes is alternated by the radius of the pipes so as to obstruct gas flow. Because of the deviation, washing water becomes a local flow without permeation / wetting of unburned carbon or soot-based deposits by washing water or washing and removal, and a large amount of washing water is used. However, there was a problem that the adhered substances could not be removed effectively.

Further, even if jet cleaning is performed with high-pressure water, the arrangement of the pipes is vertically displaced by a radius, so that the outer 1-2
The pipes in the row could only be washed with water, and even if a large amount of washing water and a long time were required, effective removal of deposits was not possible.

[0007]

In order to solve the above-mentioned problems of the prior art, the present invention focuses on the oil content and the porosity of the deposits, and a heat transfer tube of a heat transfer tube in which heat recovered gas flows outside. Spray a chemical cleaning liquid that is a mixture of nonionic surfactant and ammonium carbonate on the outer surface, and then pour water into the heat transfer tube to encapsulate it, and vibrate the water ultrasonically to cause heat transfer in the heat transfer tube. The present invention relates to a method for removing deposits on the outer surface of a heat transfer tube, which comprises simultaneously applying vibration to the outer surface and washing the outer surface of the heat transfer tube with water.

[0008]

[Function] First, by spraying a chemical cleaning liquid, which is a mixture of a nonionic surfactant and ammonium carbonate, on the adhered matter adhered to the outer surface of the heat transfer tube, the adhered matter adhered to the outer surface of the heat transfer tube is removed. Contact to dissolve the oil content in the deposit. After that, water is poured into the heat transfer tube to seal it, and the water is ultrasonically vibrated, whereby vibration is applied from the inside to the outside of the tube, so that the deposit on the outer surface of the pipe and the chemical cleaning liquid that has penetrated into the deposit are sulfuric acid. With the following reaction, CO ₂ is generated by the following reaction.

[0009]

[Chemical 1]

CO generated by the reaction of [Chemical formula 1]
₂ and nonionic surfactant cause foaming in the deposit. Due to this foaming, the adhered matter becomes porous and is physically fragile, so that the adhered matter is easily separated from the heat transfer surface. In order to further accelerate this, by applying ultrasonic vibration to the water enclosed in the heat transfer tube, by performing water washing while also applying vibration to the adhered matter on the outer surface of the heat transfer tube,
The deposit is completely removed.

[0011]

An embodiment of the present invention will be described in detail below with reference to FIG. In FIG. 1, the same parts as those shown in FIG. 2 are designated by the same reference numerals, and the description thereof will be omitted.

In this embodiment, a chemical cleaning liquid 11 containing, for example, 10 to 5% of a dissolved nonionic surfactant and 5% of ammonium carbonate is stored outside the exhaust gas economizer casing 1 for chemical cleaning. A tank 12 is installed. The chemical cleaning pipe 13 extending from the lower portion of the chemical cleaning tank 12 is connected to the water cleaning pipe 6 at a downstream side of the valve 5 provided in the water cleaning pipe 6, and A chemical washing pump 14 and a pair of valves 15 and 16 are provided in the middle of the pipe 13, and the pair of valves 15 and 16 are provided.
16 are arranged on the upstream side and the downstream side of the chemical washing pump 14.

The preheater tube 2, the low-pressure evaporator tube 3 and the superheater tube 4 (hereinafter referred to as heat transfer tubes) are provided at one end thereof with water supplied from the water tank 17 by a water pump 18. The pipes 19 are connected, and the return pipes 21 for returning the hot water to the water tank 17 are connected to the other ends of the pipes 19. An ultrasonic oscillator 21 is installed at the inlet of the supply pipe 19.

In the structure described above, the valves 15 and 16 are opened and the chemical cleaning pump 14 is driven, so that the chemical cleaning liquid 11 is passed from the chemical cleaning tank 12 through the chemical cleaning pipe 13 and a part of the water cleaning pipe 6. The chemical cleaning liquid 11 is sprayed from each nozzle 7 of the water washing pipe 6 to bring the chemical cleaning liquid 11 into contact with the deposit adhered to the outer surface of the heat transfer tube to dissolve the oil in the deposit and to penetrate the chemical cleaning liquid 11 into the deposit. Let

Thereafter, the pair of valves 15 and 16 are closed again, the chemical washing pump 14 is stopped, and the pump 18 is driven.

As a result, the water prepared in the water tank 17 is passed through the supply pipe 19 into the preheater pipe 3, the low-pressure evaporator pipe 3 and the superheater pipe 4. Excess water is collected in the hot water tank from one end of the heat transfer tube through the return pipe 20, but the water is filled in the heat transfer tube in a full state.

Next, the ultrasonic oscillator 21 is operated to transmit the vibration of ultrasonic waves to the outer surface of the heat transfer tube through the water in the heat transfer tube, and the deposit on the outer surface of the heat transfer tube and the chemical cleaning liquid permeating the deposit. 1
1 is vibrated to accelerate the reaction between the sulfuric acid in the deposit and the chemical cleaning liquid 11, and the deposit undergoes the foaming action as described in the above "Action" column.

When the valve 5 is opened, the nozzle 7 of the rinsing pipe 6 is used to wash the rinsing water with respect to the deposits on the outer surface of the heat transfer pipe which are easily separated due to the foaming and degreasing action. Is sprayed again to completely remove the deposits and the washing liquid.

[0019]

As described above, according to the present invention,
Organic matter consisting of unburned carbon that is difficult to remove only by washing with water
It is possible to completely remove deposits such as soot and ash on the outer surface of the heat transfer tube with a chemical cleaning solution that mixes nonionic surfactant and ammonium carbonate without corroding the heat transfer surface, and then by rinsing with water. It is possible to prevent draft loss and improve the exhaust heat recovery rate.

The amount of rinsing water used is 30-40 of the conventional one.
From m ³ to about 5 m ³ or less, the time and cost required for washing with water can be greatly saved.

[Brief description of drawings]

FIG. 1 is a system diagram showing a method for removing deposits on the outer surface of a heat transfer tube according to an embodiment of the present invention.

FIG. 2 is a system diagram showing a conventional method for removing deposits on the outer surface of a heat transfer tube.

[Explanation of symbols]

 1 Exhaust gas economizer casing 2 Preheater pipe 3 Low pressure evaporator pipe 4 Superheater pipe 5 Valve 6 Water washing pipe 7 Nozzle 8 Cleaning waste liquid trough 9 Discharge pipe 10 Waste liquid tank 11 Chemical cleaning liquid 12 Chemical cleaning liquid tank 13 Chemical cleaning pipe 14 Chemical washing pump 15, 16 valve 17 Water tank 18 Pump 19 Supply pipe 20 Return pipe 21 Ultrasonic oscillator

Claims (1)

[Claims] 1. A chemical cleaning liquid in which a nonionic surfactant and ammonium carbonate are mixed is sprayed onto the outer surface of a heat transfer tube through which heat-recovered gas flows outside, and water is then poured into the heat transfer tube. A method for removing deposits on the outer surface of a heat transfer tube, wherein the water is ultrasonically vibrated to vibrate the outer surface of the heat transfer tube, and at the same time, the outer surface of the heat transfer tube is washed with water.