Chemical cleaning of boiler of the hottest 660 uni

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Chemical cleaning of 660MW Unit Boiler

Hebei Hanfeng Power Plant 2 × The 660MW project is a cooperative project with Siemens. The boiler used is the world's largest "W" flame boiler. The boiler type is subcritical, primary intermediate reheat, solid-state slag removal, natural circulation drum boiler, which is manufactured by foster-wheeler company in the United States. The superheater steam flow is 2026 8t/h, and the superheater outlet pressure is 17 5MPa. According to the relevant provisions in SD guidelines for chemical cleaning of boilers in thermal power plants issued by the former Ministry of electric power and the requirements of foreign parties, the boiler heating surface must be chemically cleaned to remove oxides, welding slag, mud and sand and other pollutants generated during the production, transportation, storage and installation of equipment. Different from the currently commonly used dynamic cleaning process in China, this cleaning adopts the hot hydrochloric acid static immersion cleaning process. The process includes alkali boiling under the pressure of 345mpa, hot hydrochloric acid static immersion, nitrogen top pressure discharge, neutralization and passivation, etc. The superheater is not cleaned, but needs to be flushed and backwashed during the chemical cleaning of the boiler

2 cleaning principle and cleaning range

2 1 cleaning principle

use alkali boiling to remove oil stains and loose deposits on the surface of pipes and equipment; Hydrochloric acid cleaning is used to remove high-temperature oxide scale, corrosion products, welding slag, sediment pollution, etc

2 . 2. Cleaning scope the cleaning scope includes the water-cooled wall of boiler body, steam drum and economizer

3 small scale test of chemical cleaning

3.1 test before cleaning in order to ensure that the chemical cleaning of thermal equipment in the power station can be carried out safely and reliably, the corrosion rate measurement test and corrosion inhibition efficiency measurement test of corrosion inhibitor for chemical cleaning under static conditions were carried out before cleaning

3.2 test conditions test temperature: 70 ± 1 ℃ test piece material: steam ladle steel, economizer tube, water wall tube cleaning solution: test piece area: 15ml ∶ 1cm2 cleaning medium: hydrochloric acid (5%)

3.3 test results see Table 1 for small test results

the corrosion rate of various materials is lower than 1g/m2h, and there is no pitting corrosion on the surface of the indicator

4 cleaning

4 1 Composition of the cleaning system the boiler cleaning system is mainly composed of the temporary system and the boiler body. Jinan new era Gold Testing Instrument Co., Ltd. sincerely welcomes users to call us for consultation. The cleaning system is shown in Figure 1

4 . 2 boiler cleaning in the cleaning process includes three basic procedures: alkali boiling (at the same time as oven drying), acid pickling, neutralization and passivation, which can be specifically divided into seven stages: water washing, alkali boiling (oven drying) under 3 45MPa pressure, water washing, acid pickling, nitrogen top pressure waste acid liquid discharge. Sometimes several test pieces are made into a set of experiments to carry out strength test, nitrogen top pressure water washing, neutralization and passivation, See Table 2 for various indicators tested during cleaning

4.2.1 the water flushing demineralized water enters the boiler through the condensate system, water supply system and economizer, and supplies water to the boiler to the normal water level. The flushing water is discharged through the drain valve of the lower header of the water wall and the header at the inlet of the economizer until the drainage is clear and transparent

4.2.2 in the boiler boiling stage, according to the drug concentration shown in Table 2, the main technical parameters of the temporary system comply with gb1499.2 (2) 018 steel tubes for reinforced concrete Part 2: hot rolled ribbed steel bars, yb/t5126 (2) 003 plan for plane reverse bending test of steel bars, and the provisions and requirements of iso10065:1900 on cold bending test and plane reverse bending test. The boiler boiling drugs are prepared and injected into the boiler through the lower header of water wall and economizer. When the boiler is ignited, slowly increase the pressure to 3.45mpa within 8 hours, and keep it for 24 hours under this pressure. During boiler boiling, blowdown shall be conducted through the blowdown valve of water wall every 6 hours. After 24 hours of boiler boiling, shut down the boiler to reduce the boiler pressure. The pressure is reduced to 0.17mpa, and the waste liquid in the boiler is discharged to the waste liquid treatment system through temporary pipes

4.2.3 water flushing regulates the condensate and feed water valves, and normally feeds water to the boiler through the economizer inlet. Then discharge the waste liquid through the temporary system until the drainage becomes clear and the pH value is ≤ 9.0, and the boiler boiling is completed

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