Applying Refractometers to the on-line Measurement of Green Liquor Density
绿液密度（或总碱含量）在线精确测量最初一直是困扰制浆客户的严重问题：γ射线法不仅对操作者有辐射，而且因绿液结晶快，其检测结果严重失准；同样因为绿液结晶快，密度法根本不适用；折射法理论可行，但实际也曾遇到棱镜因结晶结垢快不能正常工作的问题。
但，自EMC发明最具革新意义的HPC-2高压清洗装置以来，EMC 公司MPR在线精确稳定测量绿液密度已有超过30年的历史，已被成功应用在无数绿液装置中。这个系统由MPR按设定时长启动，通过适配器上直径0.1毫米的“水针”清洗喷嘴，向蓝宝石棱镜喷射HPC-2泵来的高压水。HPC-2产生高达2800psi(193bar)的高压水，通过“水针”斜切清洗掉蓝宝石棱镜上的结垢层。由于保持清洁的蓝宝石棱镜，MPR可以非常精确地测量和控制绿液的密度（或总碱含量）。
Procedure for Safely Removing Sensing Head or Maintenance Plug from Electron Machine Corporation Isolation Valve Adapter
Green liquor is the dissolved concentration of sodium sulfide, sodium carbonate, and other compounds from the recovery boiler in the paper making process. Measuring its density is a critical component for the quality of the paper production.
The difficult scaling associated with green liquor results in an optical coating on the refractometer sensing head. If this scaling can be controlled to allow an acceptable duration of on-line measurement, and then effectively removed when coating occurs, the accuracy of the refractometer can be fully utilized with minimal maintenance. The primary issue then becomes the maintenance required to keep the cleaning system operating effectively.
Using inline refractometers with accompanying heated high-pressure water cleaning systems provides excellent results in effective removal of optical coatings by reducing thermal changes, minimizing maintenance, and allowing for a reliable measurement source for on-line automatic control.
The Electron Machine MPR EScan is used to measure the green liquor dissolved density, or TTA, at two stages in the process: after the green liquor dissolving tank and after the green liquor clarifier. The in-line measurement, with the refractometer sensing head installed directly in the main process lines, allows real-time control of green liquor dilution to meet target TTA set-points. The measurement is also used to indicate (and prevent) excessive green liquor density and the resulting dangerous impending crystallization within the dissolving tank.
Paper mill green liquor density measurement system MPR Escan
Electron Machine MPR Escan
Reducing the variation of green liquor solids by automatically controlling weak-wash dilution with the MPR E-Scan refractometer results in a reduction in scaling. Scaling issues are further reduced when pressurized water, heated to the process temperature, is used to effectively clean the refractometer optical components. The compound result is beneficial for both control and maintenance. It's said the only thing a pulp and paper plant doesn't reuse is the "shade the building casts". The processes used in the production of pulp and paper are very efficient when you consider the reuse of energy and by-products. The efficiency comes at a cost though - through very hostile atmospheres and demanding operating conditions for process equipment.
For example, the "kraft process" (also known as the sulfate process) is the method to convert wood chips into pulp and then to cellulose fibers. This is done by mixing the wood chips with sodium hydroxide and sodium sulphate, soaking, cooking and processing.
Here's a very basic explanation of the kraft process. Wood chips are soaked and processed in sodium hydroxide and sodium sulphate mixture known as "white liquor". After the wood chips are impregnated with white liquor, they are then cooked in digesters to break the wood down into cellulose. The solid pulp is then separated and the remaining fluid is referred to as "black liquor". Black liquor is further processed to remove solids and chemicals which are to be re-used in the pulping process. One of the final by-products is "green liquor" which contains sodium carbonate and sodium sulfide and is then reacted with lime to regenerate more white liquor.
All of these steps expose instruments, process equipment, piping, and valves to very tough environments. Electron Machine Corporation, a manufacturer of extremely rugged inline process refractometers, has been actively refining the use of refractometers for measuring green and black liquor density for over 30 years.
The scaling associated with these applications results in an optical coating on the refractometer sensing head. If this scaling can be controlled to allow an acceptable duration of on-line measurement, and then effectively removed when coating occurs, the accuracy of the refractometer can be fully utilized with minimal maintenance. The primary issue then becomes the maintenance required to keep the cleaning system operating effectively.
Electron Machine's efforts led to a system using their "almost indestructible" MPR E-Scan Refractometer combined with heated high-pressure water for cleaning. The resulting combination provides an effective removal of optical coatings by reducing thermal changes and minimizing maintenance to allow for a reliable measurement source for on-line automatic control.
If you're interested in refractometry in pulp and paper processing, look no further than Electron Machine. They have the history, the experience, and the toughest inline refractometer on the planet. The MPR E-Scan is a hybrid-digital critical angle in-line process refractometer.It is used to measure the refractive index of process fluids and may be used as an error indicator or an integral part of a complete process control system.Refractive index can be directly correlated to dissolved solids and displayed as Brix, percent, or other measurement unit.
The MPR E-Scan is a rugged, industrialized, in-line process refractometer. It directly measures the refractive index of process fluids and then displays the reading in any number of customer-desired units (Brix, Percent Solids, Dissolved Solids, SGU, R.I., etc.). This reading may be used as an error indicator or part of a complete process control system. A high-resolution color display and a 4-20mA output is standard. HART® protocol, RS-232, and RS-422 outputs are available.
Each sensing head is custom tailored and calibrated specifically for the desired process application to ensure the most accurate and useful reading. A simple 0-10Vdc signal is used to transmit the reading from the sensing head to the electronics console, ensuring a robust reading that has a minimal chance of being effected by interference. The entire package is NEMA 4X rated and designed and manufactured with the best materials for each application to provide years of trouble-free service with a minimum amount of maintenance.
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Applying Refractometers to the On-line Measurement ofGreen Liquor Density A presentation tothe Black Liquor RecoveryBoiler Advisory Committee (BLRBAC) by C.A. Vossberg, President of Electron MachineCorporation.
Download the PDFversion of "Applying Refractometers to the On-line Measurement of GreenLiquor Density" from this link.
EMC公司管道隔离阀生产制作流程
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Electron Machine Isolation Valve Adapter and Safeguard Tool Demonstration
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