Alkali recovery equipment quality appraisal

alkali recovery equipment is the core environmental protection equipment in the paper industry. It is used to extract alkali from pulping black liquor and recycle it to achieve pollutant emission reduction and efficient resource utilization. Its work flow includes black liquor evaporation and concentration, combustion causticization, green liquor clarification and other links, which can achieve an alkali recovery rate of more than 95%, significantly reducing enterprise production costs and environmental pollution. Under the carbon peak and carbon neutrality goals of the papermaking industry, alkali recovery equipment has become a key support for green manufacturing through energy cascade utilization and waste resource utilization. Compared with the traditional alkali recovery process, modern intelligent equipment reduces energy consumption per ton of pulp by more than 30% through DCS control system and new evaporator design, promoting the transformation of the papermaking industry into a low-carbon one.

As papermaking capacity expands and environmental protection requirements become stricter, quality disputes over alkali recovery equipment occur frequently. Judicial disputes focus on: whether the equipment meets technical indicators such as alkali recovery rate (such as ≥95%) and steam energy consumption (such as ≤1.5 tons/ton of pulp) stipulated in the contract; whether there are shutdown accidents caused by material corrosion and scaling; whether the control system is stable and reliable; and the correlation between quality problems, environmental pollution accidents, and economic losses, etc. In such cases, the quality appraisal of alkali recovery equipment uses black liquor composition analysis, thermodynamic performance testing and other technical means to provide a scientific basis for the court to determine liability and loss compensation, and to help the paper industry green transformation and compliance.

Zhongke Testing is a product quality appraisal service organization registered with the court. It can provide quality appraisal services for alkali recovery equipment. It has a professional appraisal team and advanced instruments and equipment to provide fair and accurate appraisal results for the quality appraisal of alkali recovery equipment.

Alkali recovery equipment quality identification technical methods include:

1, appearance and structural inspection

Check whether the materials of key components such as evaporator tube bundles and combustion furnace linings (such as 316L stainless steel, nickel-based alloys) meet corrosion resistance requirements, and whether there is scaling or perforation on the surface.

2, thermodynamic performance test

measure the temperature, pressure, flow and other parameters of the black liquor evaporation process, and calculate the evaporation efficiency and steam consumption. Analyze the thermal efficiency of the combustion furnace and verify whether the alkali recovery rate reaches the design value.

0Observe the microstructure of the tube bundle scale layer through a scanning electron microscope and analyze the scale components (such as silicon and calcium compounds). Conduct coupon corrosion tests to evaluate the annual corrosion rate of materials in a black liquor environment.

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A paper mill of the applicant signed an "Alkali Recovery System Procurement Contract" with an environmental protection equipment company of the respondent, agreeing to purchase a set of alkali recovery equipment capable of processing 500 tons of black liquor per day. After the equipment was put into operation, the alkali recovery rate continued to be lower than 90% (contract requirement ≥95%), and the evaporation system frequently shut down due to tube bundle scaling. The paper mill believed that the equipment had design defects and demanded compensation for the loss caused by the production shutdown. The equipment company argued that the problem was caused by abnormal composition of the black liquor or improper operation, and both parties went to court. The court entrusted a third-party appraisal agency to conduct quality appraisal of the equipment involved in the case.

Identification and analysis results:

The quality analysis expert group discussed and comprehensively analyzed the relevant information of the "alkali recovery equipment", contract technical agreement, on-site investigation case materials and other data, and made the following quality analysis opinions:

1. The material of the evaporator tube bundle in the alkali recovery equipment involved is 304 stainless steel (contract requirements) 316L), insufficient corrosion resistance leads to scaling on the inner wall. There are many cracks in the refractory bricks lining the combustion furnace and they have partially fallen off, affecting the thermal efficiency.

2, the DCS system of the alkali recovery equipment involved in the case delayed its response to black liquor concentration fluctuations for up to 30 seconds (design requirement ≤10 seconds), resulting in out-of-control evaporation parameters. The safety interlock device failed to shut down in time when the liquid level of the evaporator was too low, which aggravated the dry burning and scaling of the tube bundle.

Alkali recovery equipment quality appraisal report should include the following content:

1. Information on the appraisal client and the appraised party.

2. Testing items, sampling methods, testing methods and equipment.

3. Test results and analysis.

4. Quality evaluation conclusion.