After market research, technicians from Supmea Flowmeter Manufacturer found that among the complete sets of equipment imported from abroad, most of the liquid measurement uses electromagnetic flowmeters.
After market research, technicians from Supmea Flowmeter Manufacturer found that among the complete sets of equipment imported from abroad, most of the liquid measurement uses electromagnetic flowmeters. Domestic large and medium-sized papermaking enterprises have gradually begun to complete the process of replacing traditional differential pressure flowmeters with electromagnetic flowmeters. At the same time, they have proposed higher usage and measurement performance requirements to manufacturers, thus promoting the technology of electromagnetic flowmeters. progress.
As environmental protection regulations have become more and more stringent in recent years, most papermaking companies have built waste liquid treatment processes in addition to the main papermaking process. The survey found that electromagnetic flowmeters are used in almost all sections of the paper mill.
1. Material preparation process
The main task of the material preparation section is to make different raw materials into premium materials. The electromagnetic flowmeter is mainly involved in the flow measurement of polished slurry, water and acid or alkali during the pulping process. Generally, the temperature of the slurry after mechanical polishing should reach 80°C. When pulping is made from materials such as wood or grass, it often goes through a cooking process. Since the cooking liquid is an alkali such as Ca(OH)2 or Na0H solution, and the slurry is alkaline, electromagnetic flowmeters mostly use high-temperature resistant polytetrafluoroethylene linings and split-type structures. When selecting electrode materials, consider choosing materials with strong corrosion resistance. Alkaline slurries generally use Hastelloy Hc, titanium Ti and other materials, and tantalum electrodes must not be used; if the requirements are not high when measuring acidic slurries, acid-resistant steel 316SS can also be used.
Usually, many domestic enterprises use waste paper pulping, that is, the waste paper is pulped and then washed and bleached. The electromagnetic flowmeter here is mainly used to measure the water flow rate after pulping. Most of the water is nearby river water that is slightly treated before participating in the operation, so the water quality is poor, but it is not corrosive. The electromagnetic flowmeter can use conventional rubber lining and stainless steel electrodes; while for the deinking agent ( Common deinking agents include Na0H, Na2SiO3, Na2O2 or H2O2). When measuring, the electrodes and linings of the electromagnetic flowmeter must be selected carefully. Taking a typical 35-ton paper mill as an example, a large number of electromagnetic flowmeters are used in the material preparation process, roughly between 50-60 sets.
2. Screening of the bleaching section
Sort based on the quantity used, and the screening of the washing section should be *. Taking a typical 350,000-ton paper mill as an example, the number of electromagnetic flowmeters used in these two sections must reach about 250 sets.
The electromagnetic flowmeter is used to measure the inflow of each pulp tank from each material preparation workshop into the papermaking workshop and the flow measurement point outflowing from each pulp tank into the pulp mixing tank. There are five kinds of pulp (slurry, pulp, Deinked pulp, CTMP, machine pulp, damaged liquid pulp) participate in the pulp preparation process. The temperature of the machine slurry and CTMP slurry here is as high as 50-80°C, and the flow meter lining material should be considered to be PFA or PTEE.
In the slurry proportioning process, each manufacturer uses different slurry proportioning concentrations to obtain paper of different qualities. However, the finished product is often unqualified due to a slight deviation of a slurry, resulting in greater material and economic losses. So eachThe production plant attaches great importance to this link. An electromagnetic flowmeter is installed in each proportioning pipeline to measure the instantaneous and total flow rate flowing into the main slurry distribution pipe. At the same time, an online concentration meter is installed at the lower end of the slurry distribution pipe. To test the slurry mixing effect. If there is a deviation from the predetermined concentration, immediately adjust the opening of the valve to adjust the corresponding slurry flow rate. This city does not require electromagnetic flowmeters to have high accuracy, but also requires good repeatability and dynamic response. In the above situations, the diameter of the electromagnetic flowmeter is generally between DN50-DN150.
The screening process after pulp preparation is commonly known as the papermaking process. Pulp concentration often affects flow measurement during this process. We found that pulp with a concentration greater than 3% can use conventional low-frequency square wave excitation frequency (such as 25Hz) or dual-frequency excitation to improve the sloshing phenomenon. Taking the DN300 electromagnetic flowmeter to measure corrugated cardboard with a concentration of 3.5% as an example, when using a conventional 1/32 power frequency, the instantaneous flow fluctuation is as high as 10.7%. An electromagnetic flowmeter with a changeable frequency is selected to change the excitation frequency. At 1/2 power frequency, the shaking amount is improved to 1.9%, and the effect is very obvious. In the papermaking section, due to the need to monitor the flow of cooling water, alum and talcum powder during the pulp preparation and papermaking process, the number of them used is the largest in the papermaking factory, reaching about 200 sets in this case.
In order to ensure that the whiteness of the paper is uniform and detailed, different additives, dispersants and bleaching agents are added. Just like the use of additives in the food industry, these additive liquids have a small flow rate and are highly corrosive, so most of them use PTEE liners and PFA liners. Because of its strong oxidizing properties, H2O2 is often chosen as a bleaching agent by paper mills, but H2O2 is particularly corrosive to metal materials. For anti-corrosion considerations, engineers like to use Pt as an electrode material. However, actual use has proven that when the process pressure is less than 0.3MPa, the Pt electrode will react with H2O2 and form a layer of aerosol on the electrode surface, which we call a catalytic reaction. At this time, the output signal will fluctuate greatly. But if you choose tantalum (Ta) electrode, there will be no above problems. If we choose a tantalum electrode when switching to NaOH solution, the situation is not so optimistic, because the alkali solution will cause surface effects on the tantalum electrode. Data from the HUAHO calibration laboratory shows that when measuring ordinary water, the zero point of tantalum electrodes changes dozens of times more than other electrodes. Special attention should be paid to concentricity when installing small-diameter electromagnetic flowmeters. In the above example, using a DN10 small-diameter electromagnetic flowmeter to measure these additives can achieve ideal results. In foreign paper production lines, there are many examples of Coriolis mass flow meters being used in these situations.
After years of practice, electromagnetic flowmeters generally use PTFE or other fluoroplastic liners in the papermaking field: electrodes are selected according to different liquid properties. Statistics show that more than 85% of the thousands of electromagnetic flowmeters used by HUAHO in the papermaking industry use PTFE, and the actual results are satisfactory. Although some important small flows in foreign paper millsDeriolis mass flow meters are used for part of the measurement, but electromagnetic still occupies a dominant position in liquid measurement in the paper industry. The vast majority of usage problems arise from initial selection and improper installation. Such as mismatching of electrodes or lining materials (as shown in the table), as well as dissatisfaction with the pipe, insufficient straight pipe length, non-concentricity when installing small diameters, etc. These are often the main factors that prevent the electromagnetic flowmeter from operating normally.
In the future, the requirements for the production process of the papermaking industry will become higher and higher. From the perspective of energy and environmental protection, it needs to be continuously improved to reduce the waste of materials and environmental pollution during the production process. Therefore, in the future, the papermaking industry will The process requirements for flow meters will also become more stringent, and it is expected that more advanced measuring instruments will come out soon. As a professional R&D flowmeter manufacturer, Heshunda Flowmeter Manufacturer has been adhering to the production philosophy of creating a brand with quality and seeking development with brand over the past few years. It has persisted in overcoming difficulties and continuously developed new technologies and products to provide We provide our customers with products that are of reliable quality and meet their needs, and have also established long-term cooperative relationships with many manufacturing companies. All colleagues at Heshunda look forward to setting sail with you.
Hangzhou Economic Development Area，Hangzhou 310018，China
