CN100436647C - Scale eliminating method for casing pre-heater - Google Patents

Abstract

The present invention discloses a method for cleaning scabs of a sleeve pipe preheater, which uses diluted sulfuric acid for cleaning scabs of a sleeve pipe preheater. The method for cleaning scabs of a sleeve pipe preheater comprises: diluted sulfuric acid for cleaning scabs of a sleeve pipe preheater is firstly filled from a last-stage sleeve pipe and discharged from a first-stage sleeve pipe so as to clean the sleeve pipe preheaters; the cleaning is carried out repeatedly, until the scab in the last-stage sleeve pipe is clean; thus, the scabs in the sleeve pipe preheater are cleaned. The present invention has the advantages that the quantity of the sleeve pipe preheaters can be increased so as to replace autoclaves; the first-stage sleeve pipe is used instead of a first-stage autoclave for preheating so as to save the construction investment by about 3 million yuan; when a five-stage sleeve pipe preheater is changed into a six-stage sleeve pipe preheater, the live steam can be saved by about 0.12t per ton of aluminium oxide, and the live steam can be saved by 96 kt every year for an alumina plant with the annual output of 800 kt, namely that the production cost can be saved by about 7 million yuan every year; the method for cleaning scabs of a sleeve pipe preheater has the advantages of favorable cleaning effect, and has favorable effect on scab treatment for hot sections; acid is filled from the front end and the rear end for cleaning so as to reduce the corrosion of diluted sulfuric acid to seamless steel pipes.

Description

Cleaning method of casing preheater scab

Technical field:

The invention relates to a method for cleaning scabs on a casing preheater used for raw ore pulp preheating in alumina production, and belongs to the technical field of casing preheaters.

Background technique:

In alumina production, when high-temperature and high-pressure dissolution is used, a large amount of secondary steam is generated after the stripped pulp undergoes multi-stage flash evaporation. This secondary steam is not discharged outside, but is used for preheating the original pulp to achieve energy saving Reduce consumption and effectively protect the environment and the safety and health of labor production. In the prior art, there are two methods for indirect preheating:

Indirect heating autoclave preheating: Although this equipment is an advanced and very effective equipment for indirect heating of high-pressure dissolution; but it has its own weight and has a transmission stirring device, heating tube bundle and lubrication system, etc., that is, the system is relatively complicated. ; As a result, the investment is large, the operation is difficult, the maintenance and repair, and the workload of scab cleaning are large, and the heat transfer coefficient is low in addition.

Casing preheating: The inner and outer pipes of the pipe preheater are made of seamless steel pipes, the inner pipe is the solution flow channel, and the outer pipe is the heating steam flow channel. Compared with the pressure cooker, it has a higher heat transfer coefficient and less construction investment. It has the advantages of low maintenance and overhaul, small cleaning workload and compact structure; however, as the number of pipeline preheating stages increases (that is, the length of the pipeline increases), as the running time advances, the scarring at the high-temperature end will continue to thicken, even if Using the treatment method in the prior art, the scabs in the high-temperature section still cannot be cleaned, resulting in a significant reduction in the number of heat transfer systems, an increase in pipeline resistance loss, and even pipeline blockage, forcing production to be uncontinuous stable operation. Therefore, in the prior art, there are at most five stages of casing preheater pipelines in the mechanically stirred indirect heating dissolution system.

Invention content:

The object of the present invention is to provide a method for cleaning the scabs of the casing preheater to better clean the scabs in the casing, so as to overcome the shortcomings of the prior art.

The present invention is constituted like this: a kind of cleaning method of casing preheater scab, it adopts dilute sulfuric acid to clean casing preheater scab, will be used to clean the dilute sulfuric acid of casing preheater scab, first by Inject the last-stage casing, discharge from the first-stage casing for cleaning, and repeat the cycle of cleaning until the scars in the last-stage casing are cleaned, so that the cleaning of the casing preheater scars can be completed; When there are scars remaining in the first-stage casing, the dilute sulfuric acid used to clean the casing preheater is injected from the first-stage casing and discharged from the last-stage casing, and the cleaning cycle is repeated until Clean the residual scabs in the first-stage casing to complete the cleaning of the casing preheater scabs; the pH value of dilute sulfuric acid for cleaning the casing preheater scabs: 3-6.

The present invention has the following advantages: 1. The cleaning effect is better, especially the scarring treatment effect on the high temperature section is better;

2. The number of casing preheaters in the existing high-pressure dissolution system can be increased to replace the pressure cooker, and the construction investment can be saved by about 3 million yuan by using the first-level casing instead of the first-level pressure cooker for preheating;

3. Increase the five-stage casing preheater to more than six stages, and save about 0.12 tons of new steam for every ton of alumina produced. An alumina plant with an annual output of 800kt can save 96kt of new steam every year, that is, it can save production every year The cost is about 7 million yuan;

4. The first and last ends are cleaned with acid, which reduces the corrosion of dilute sulfuric acid on seamless steel pipes.

Description of drawings:

Accompanying drawing 1 is the structural representation of the present invention.

Detailed ways:

Embodiments of the present invention: the present invention can be improved on the existing technology. When the scarring of the casing preheater needs to be treated, it is cleaned with dilute sulfuric acid with a pH value of 3 to 6, which will be used for cleaning the casing preheater. The dilute sulfuric acid scabbed on the heater is firstly injected from the last-stage casing and discharged from the first-stage casing for cleaning for 1 hour until the scars in the last-stage casing are cleaned; when the above cleaning work is completed , if there are still scars in the first-stage casing, the dilute sulfuric acid used to clean the casing preheater is injected from the first-stage casing and discharged from the last-stage casing, and the cleaning cycle is repeated until Clean the remaining scabs in the first-stage casing, so that the cleaning of the casing preheater scabs can be completed.

Claims (3)

1. purging method that cannula primary heater scabs, it is characterized in that: it adopts dilute sulphuric acid cannula cleaning preheater to scab, to be used for the dilute sulphuric acid that the cannula cleaning preheater scabs, at first inject, discharge from first step sleeve pipe and clean by the last step sleeve pipe, wash cycles so repeatedly, up to scabbing in the last step sleeve pipe cleaned up, can finish the cleaning that cannula primary heater is scabbed like this.

2. the purging method that cannula primary heater according to claim 1 scabs, it is characterized in that: when in the first step sleeve pipe during also residual scabbing, to be used for the dilute sulphuric acid that the cannula cleaning preheater scabs, inject, discharge from first step sleeve pipe from the last step sleeve pipe, wash cycles so repeatedly, residual scabbing cleans up in first step sleeve pipe, can finish the cleaning that cannula primary heater is scabbed.

3. the purging method that cannula primary heater according to claim 1 and 2 scabs is characterized in that: the pH value of the dilute sulphuric acid that the cannula cleaning preheater scabs is: 3～6.

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