6 factors to consider in the anti-corrosion renovation of old chimneys
The basic requirement for anticorrosion of old chimneys is that when condensed acid appears on the inner wall of the chimney, the lining of the chimney should not be corroded and lose its structural safety within the designed service life, and it should not be damaged due to corrosion of the lining. The reinforced concrete outer cylinder wall endangers the bearing capacity of the chimney structure. When the reinforced concrete outer cylinder wall is corroded, it directly affects the structural safety.
Before the anti-corrosion treatment of the chimney is carried out, in order to ensure the safety and reliability of its use, a unit with the qualification for reliability testing and appraisal of the building structure should be requested to evaluate the reliability of the structure of the chimney. At present, the main components of materials suitable for the anti-corrosion transformation of old chimneys in China are the combination of organic resin and inorganic materials. Cracks are prone to occur. Their component proportions will seriously affect the performance and durability of anti-corrosion materials, which should be comprehensively considered in the anti-corrosion renovation of old chimneys.
The anti-corrosion transformation of old chimneys needs to consider the following 6 factors
(1) Service life of old chimney after renovation
The design life of the chimney is usually 35 years, and the general economic operation life of thermal power equipment is about 25 years. The chimney is the last link in the operation of the generator set. Due to the continuous improvement of environmental protection standards, the chimney is gradually regarded as a piece of equipment in the thermal power generation system.
First of all, it should be clear how many years the transformed unit may run, so as to determine the anti-corrosion standard and anti-corrosion design life of the chimney. For a chimney that is expected to run for 30 years and a chimney that may run for 10 years, the construction process for anti-corrosion transformation of the chimney lining is definitely different, and it cannot be simply required by the anti-corrosion design standards for new chimneys.
(2) The original smoke letter structure type
A few years ago, the supporting chimneys of non-desulfurization units (including adding GGH after desulfurization) in my country were generally single-tube chimneys or sleeve chimneys. The inner wall of the single-tube chimney is made of brick or double-slip cement mortar. The inner cylinder of the sleeve chimney is available in brick and steel. Before the anti-corrosion transformation, the structural type of the original smoke solid lining must be found out. Generally, the anti-corrosion requirements of wet chimneys are not considered, and suitable anti-corrosion materials are selected for different lining surfaces. For the sleeve chimney, the inner wall of the steel chimney can only be added with acid-resistant cement or paint as a water barrier.
For the chimney that used glazed acid-resistant bricks in the past, since the water absorption rate of the acid-resistant bricks purchased in China is 12% to 20%, it is far from solving the problem of anti-corrosion of wet chimneys. After lining, it was rebuilt with foam ceramic tiles referring to the experience of Jinzhushan Power Plant and Xiangtan Power Plant. For the single-tube chimney, whether the lining is brick or the concrete surface formed by double sliding, it is necessary to apply 2-3cm acid-resistant sand frame to form an anti-corrosion layer for water and gas insulation.
(3) Cleaning the inner wall of the chimney
It is generally brick masonry, mortar plastering and steel inner cylinder. In the renovation of the old chimney, the dust accumulation and defects on the surface of the inner cylinder should be cleaned first. Due to the uneven surface of the brick lining, and some bricks are damaged, it must be cleaned by sandblasting or high-pressure water spray, and then the defects are filled. If the coating is used for anti-corrosion, it cannot be cleaned by water washing, because after water washing, the lining surface must be dried before spraying, so the construction time will be very long.
(4) Applicable operating conditions
At present, in many desulfurization units in operation, the flue gas is provided with a bypass, the working conditions of the chimney exhaust are relatively complex, and the anti-corrosion design of the exhaust pipe is relatively difficult. The owner generally proposes that the anti-corrosion coating should be suitable for the alternate operation of desulfurization conditions (wet flue gas, 45-50°C) and non-desulfurization conditions (dry flue gas, U5°C). It should be ensured that the expansion is reversible and can maintain good elasticity under the working temperature environment of 145°C for long-term operation of the chimney, and it should be able to withstand a high temperature of 180°C in a short time (half an hour each time, 3 times a year). Many organic material-based coatings are difficult to meet these requirements. If the desulfurization unit does not have a bypass in the near future, the flue gas of the chimney will not be mixed and discharged, and the anti-corrosion design of the exhaust pipe will be simpler.
(5) Schedule arrangement
For 200-300MW units, two boilers generally share one chimney. The anti-corrosion transformation of the chimney lining can only be carried out when the two boilers are scheduled to be out of service at the same time through the power dispatch plan. Generally, the entire transformation project can only be completed within 45 days. Therefore, the impact of severe cold in winter and rainy summer on the construction of anti-corrosion projects should be considered, and if necessary, heating or awning should be added during the construction process.
(6) On-site construction conditions
Since the old chimney is to be reconstructed for anticorrosion, the construction site is relatively small. During the construction of the renovation project, the stacking and transportation of engineering materials and equipment inside the chimney will be restricted. If the steel tube is added to the old chimney, the implementation conditions of the steel inner tube on-site processing site, installation, welding, and hoisting platform in the chimney should be considered.
