How many paper chemicals do you know and how to use it?

As we all know, compared with the developed paper-making countries in Europe and America, due to the shortage of land resources in China, especially the shortage of forest resources, we must protect limited forest resources. Therefore, the urgent issue that chinese paper industry must be face is : how to use artificial fast-growing forests to produce short fibers and recycled fiber/waste paper, by the way, using fine chemicals can help paper workers effectively alleviate and solve this problem.

So here let us learn what exactly is fine chemicals?

Fine chemicals mainly refer to chemicals used in the wet-end flow system of paper machines. Everyone knows that the wet end of the paper machine is a study of the various materials in the paper stock (slurry circuit and slurry circuit) in the process of water filtration, retention, forming and white water circulation, water, fiber and other additives. The science of interaction and action law; it is also a science to study the interaction between various additives and paper components and their effects on paper machine performance and product quality. It can be imagined that the wet end system of a paper machine is like a black box. Although we can't directly see what changes and reactions have occurred in the eye, we can interact with each other through a series of wet theory of paper machine. Mechanism guidance and extensive practice and exploration, and through the experience gained using a variety of different chemicals, we can indeed see the obvious changes in the system after the addition of chemicals. So we say that the wet end chemistry of the paper machine is "all things you can't see affect what you can observe."

In general, paper machine wet-end chemicals can be easily divided into two categories, functional drugs and process drugs. As the name implies, functional drugs can improve certain functions of paper and paperboard by using such chemicals, most typically by using a sizing agent to impart resistance to water intrusion by the sizing agent, which facilitates printing and writing; Process drugs are mainly used to improve the operating efficiency of the paper machine and ensure the smooth progress of the production. The most typical representative is the microbial control agent. Reasonable and correct use of the microbial control agent can improve and maintain the cleaning environment of the paper machine, reduce the paper break and Extend the cycle of secondary planned shutdown and cleaning, and finally achieve the effect of improving operational efficiency.

But how we can make the best use of the chemicals?

First, choose or consult a qualified chemical supplier or ask them to recommend suitable chemicals according to the characteristics of their paper machine and production process, the structure of raw and auxiliary materials, and the characteristics and needs of the product. The second is the production site. The technical and operational personnel should understand and master the methods and skills of using chemicals correctly. The key is to set and control the parameters of the paper machine and slurry within a reasonable range to meet the requirements of normal use of chemicals. The best use of chemicals in order to get the best performance; the third is that when conditions permit, especially for certain special chemicals, it is vital that the drug supplier cooperates with and provides high-quality on-site service. , including system testing (data monitoring and testing) and tracking, analysis of paper diseases and paper breaks. For process chemicals, it is not a "sacred water", usually it can only play the role of "icing on the cake", Noted: Chemicals are not omnipotent, so we should give reasonable expectations.

The interrelationship between the various chemicals in the wet end of the paper machine is like a chain, affecting and restricting each other. In the entire chain, the retention and drainage aids usually play a very important role. Perhaps everyone will ask why the retention and drainage system of the paper machine is the most critical chemical for modern paper machines, especially high-speed paper machines.

● This is because modern paper machines are running faster and faster. According to China's national conditions, the fiber materials we use are getting worse and worse. More and more chemical additives are added to the slurry. The system is becoming more and more complex, the amount of clean water is getting less and less, and the requirements for discharging sewage are getting more and more

● In order to effectively solve these near-demanding conditions, it is necessary to properly and correctly select the retention and drainage system and use these correctly. Retention and drainage aids, especially for highly enclosed systems, need to consider and use retention and drainage aids that are suitable for systems with high electrolytes.

● We know that the retention of good fibers, fine fibers, fillers and various additives in the paper not only reduces the loss of fibers/additives and accumulation in circulating white water, but also saves/reduces operating costs; clean flow The delivery system (the lost chemicals usually cause a lot of foam and some deposits), which lays a good foundation for improving the efficiency of the paper machine, reducing paper disease and paper breaks.

● Emission of relatively low fiber content and chemical residues in white water to reduce the load on wastewater treatment plants, easier reduction of COD and BOD content, and the content of chemicals such as metal salts/electrolytes and nitrogen, as well as lowering the cost of wastewater treatment may.

● Therefore, every papermaker should understand this and properly manage and use the retention and drainage system to ensure that the machine runs continuously and for a long time and obtains good quality, stable products and low quality. Sewage treatment costs. Due to the length of the relationship, we will focus on the system microbial control technology for the application of retention and drainage aids.

1 Proper use of microbial control agents

Microbial control is critical in a good and reasonable paper machine retention system. Fungicides – as the name implies, are agents that use physical and chemical methods to kill bacteria and microorganisms. In most paper machine operating systems, the purpose of adding fungicides is to control and inhibit the growth of microorganisms/bacteria in the slurry, white water/clear water, excipients and additive systems and to reduce the occurrence of spoilage of the slurry. The bactericide is a process control drug; for paper and paperboard for special packaging foods and liquid packaging paper for special purposes, the purpose of adding bactericide is to control the finished paper in addition to the above objectives. The amount of certain bacteria and microorganisms or spores, at which point the fungicide becomes a special functional drug.

The bactericide can be simply divided into two major categories: oxidizing bactericides and non-oxidizing bactericides; non-oxidizing bactericides can also be subdivided into bactericides and preservatives according to their reaction mechanism.

The main mechanism of action of fungicides can be described by the following terms:

● Surface-active, the drug dissolves and penetrates the cell wall to disintegrate the cells.

● Surface-linked/encapsulated type, the drug destroys the cell wall and cell membrane, causing the cells to lose their breathing or excretion function.

● Enzymes/enzymes that inactivate cells or are neurotoxic.

● Breeding control type, the drug penetrates into the cell by means of a surface-active fungicide, destroying the metabolic function of the cell and making it lose its reproductive ability. Strictly speaking, it is a preservative.

● Oxidized bactericides mainly use the mechanism of redox, which causes cells to lose electrons to be oxidized and die rapidly.

The prerequisite for the microbial control agent to achieve maximum effect is to properly select the fungicide:

Primary selection of fungicides:

● The basic situation of the production system is investigated, which requires the paper mill to take it seriously and provide convenience.

Including: the type and quantity of various microorganisms present in the system, activity and distribution, etc.; the pH, temperature, conductivity and redox potential/ORP of the slurry, white water and auxiliary materials in the system, especially the flow delivery system; At present, the paper machine mainly faces problems when it runs, and the time and frequency of the paper machine plan to stop cleaning.

● When choosing a drug, consider avoiding the possible adverse effects of the drug on the environment.

● Adverse reactions between various fungicides and possible adverse reactions with other papermaking chemicals and additives should also be avoided.

Determine the most cost-effective product from several candidate fungicide grades/products – the biocide selection test:

● Select one or several suitable fungicides by arranging the toxicity test of the drug on the test sample.

● Ensure that the fungicide reaches a certain concentration in the slurry.

● Ensure that the contact time of the fungicide with the slurry is in accordance with the conditions at which the fungicide is actually added.

● Friendly reminder: In the short circulation system of the wet end of the paper machine, the direct use of oxidizing biocide should be avoided to avoid the possibility of affecting the performance of the sizing agent and dye. In addition, some bactericides may induce foaming, especially When using a charged fungicide, avoid adding it to chemicals that are oppositely charged.

● The pH, temperature and ORP of the system will directly affect the use of the fungicide. High pH and temperature will cause the decomposition of the fungicide and lose its bactericidal function. Some fungicides are very sensitive to the ORP of the system.

Evaluation of the use of fungicides:

Whether the problems caused by microorganisms in the main paper machine system have been effectively improved:

● Mortar deposits: Whether paper breaks caused by pulp or paper disease have been slowed down and controlled; whether the number of microorganisms in the system has been effectively suppressed.

● Changes in the operating efficiency of the paper machine: Whether the time, number of times of shutdown, and the time of loss of effective operation caused by the slurry are reduced.

● The processing cost is reasonable.

2 Proper use of chemicals for system cleaning

No matter how perfect the microbiological control of the paper machine system is designed, and even how thoroughly the biocide solution is carried out, after the paper machine runs for a while, the paper machine will come due to the problem of microorganisms, sediments or adhesives. The dirtier it is, so it is necessary to carry out the necessary and reasonable cleaning.

Through cleaning, the following effects are achieved:

● Can further improve the running capacity of the paper machine

Reduce system fluctuations; reduce breaks; reduce unplanned downtime and time; improve dehydration.

● Improve product quality

Reduces holes and spots; improves moisture distribution over the full width of the sheet; improves sheet strength; reduces powder loss.

● Reduce direct production costs

Reduce the wear of the forming fabric; reduce corrosion; reduce the amount of chemicals used.

In order to help you further understand the role of cleaning agents and the correct use of cleaning agents, we can classify the commonly used cleaning agents and cleaning methods as follows:

Depending on the nature of the drug itself, cleaning agents can generally be classified into three categories: alkaline cleaners, acid cleaners, and other special purpose cleaners.

Depending on the way they are cleaned, they can also be divided into: heated chemical string washing (Boilout), foam cleaning.

Let us introduce the main components of the common cleaning agent and the control requirements of the cleaning process:

(1) Alkaline cleaning agents mainly use chemicals such as penetrants, surfactants, dispersants and chelating agents mixed with caustic soda for short circulation of the wet end of the paper machine and even for chemical string washing of the long circulation system.

The key to alkaline cleaning is to control the concentration of the cleaning solution, pH, temperature, and cleaning time.

● The concentration of the drug should be based on the degree of contamination of the system. For specific dosages, please refer to the product manual.

● The pH required to prepare the cleaning solution is above 12.

● The temperature of the cleaning solution should be controlled above 60 °C when the conditions permit.

● Ensure that the cycle time of the drug is not less than 60 minutes.

● If the cleaning process cannot meet the drug concentration, pH and temperature conditions at the same time, the cycle cleaning time of the drug should be extended, at least not less than two hours.

(2) Acid cleaning agents are also mainly used in the short-cycle or long-circulation system of the paper machine by using chemicals such as penetrants, surfactants, dispersants, corrosion inhibitors and chelating agents mixed with acid or independently used in paper machines.

The main points of acid cleaning are:

● Insoluble precipitates such as calcium carbonate can be removed from the system.

● The concentration of the drug should be determined according to the degree of contamination of the system. For specific dosages, please refer to the product manual.

● The required pH is between 3 and 3.5.

● In order to avoid possible corrosion of the system equipment during the pickling process, keep room temperature during pickling.

● The time should be controlled no more than 1 hour.

The more commonly used special purpose cleaning agents are:

Solvent-based cleaner: It is mainly used to remove the deposit of dry solid surface sizing and dry-solid coatings containing polyvinyl alcohol.

Foam cleaning agent containing hydrogen peroxide: mainly using micro-bubbles generated by hydrogen peroxide released by medicine to clean paint or stubborn deposits, mainly used for cleaning paint loading system and storage tank.

The role and main use of foam cleaning:

Foam cleaning is mainly used to solve the problem that heating chemical string washing can not be cleaned, such as various types of pulp pool; wet end frame, roller, forming wire; felt and dry net; fiber recycling system.

Evaluation of the effect of heating chemical string washing:

In order to achieve the desired cleaning effect, the entire process of heating chemical string washing must be closely monitored and tested for relevant parameters, including: pH, temperature, time, conductivity (solid content), alkalinity, acidity, chelating agent Analysis, safety, etc. of heavy metals (calcium, barium, aluminum, iron, etc.) in the residue and solution.

The basic content that needs to be monitored includes: the trend of various parameters to ensure the efficiency of cleaning; summarize the results of chemical shampoo with written documents; take photos of important parts, and organize follow-up suggestions for suggestions.

3 Important matters that should be paid attention to when using microbial control and system cleaning agents

● Before using the chemical, you should carefully read the drug instruction manual and safety data sheet (PIS & SDS) provided by the chemical supplier.

● Before starting the dosing procedure, check and confirm that the drug storage tank, metering pump, dosing line, and the point of the addition point are leak-free.

● When using two different chemicals in the same equipment or pipeline, do not switch or mix easily. Consult the chemical supplier or wash thoroughly with water or solvent before switching the second chemical.

● When adding a chemical containing irritant and corrosive ingredients such as fungicides and cleaning agents to the drug storage tank, the operator should wear appropriate protective equipment such as rubber gloves according to the requirements on the product safety data sheet. Protective glasses, etc.

● When a chemical leak is discovered, the relevant personnel should be notified immediately to take measures to prevent leakage and clean up the leak site according to the guidelines on the product safety data sheet.

● Almost all chemicals can irritate people's skin, especially the eyes. Therefore, the exposed skin and eyes of the operator should not be in direct contact with the drug to avoid injury.

● In case of accidental splashing of chemicals on human skin or eyes, immediately rinse the skin surface or eyes with plenty of water and send it to the hospital for further treatment.

● If you accidentally enter the entrance, you should immediately use the milk or water to enema and promptly send it to the hospital for further treatment according to the guidelines of the product safety data sheet.