7.10 ULTRASONIC ANALYZER

Transcription

1 ON-LINE CONCENTRATION (RED LIQUOR MEASUREMENT) PAGE 1 OF 6 APPLICATIONS OF ULTRASONIC IN-LINE ANALYZERS IN THE PULP AND PAPER INDUSTRY CHEMICAL PULPING (SULFITE PROCESS) The Sulfite Mills produce a pulp that can be used to make toilet tissue, paper towels, food fillers, and find top quality paper. SULFITE PULPING The pulp and paper industry uses two major chemical pulping process: the Kraft (sulfate) process, and the sulfite process. This process (often also referred to as the acid-sulfite process) involves high-acid cooking liquor and a substantial chemical plant and recovery process. The sulfite process may use an ammonia, calcium, sodium, or magnesium base. Many magnesium sulfite pulp mills have installed a chemical recovery process. Upon the combustion of spent magnesium base liquor, magnesium oxide and sulfur dioxide are produced. We have performed several tests with the following starting points: The red liquor must be analyzed in a 2 inch line or 3 inch line. The temperature during normal operation is between 100 C and 120 C (212 F to 248 F). The pressure is more than 2 bars, with a maximum of 10 bars. The proposed in-line analyzer should read near zero during washing with water. The temperature during washing is 100 C (212 F). SOUND SPEED MEASUREMENTS Sound speeds were measured with our standard MP42 cell attached to a closed chamber of approximately 65 ml. The Model 8100, connected to the sensor, measures twice per second (both temperature and sound speed), as well as the attenuation of the ultrasound. These measurements were logged during the entire test. The cell with sample was heated to 120 C (212 F), and while gradual cooling took place, all measurements were recorded under gentle stirring of the sample inside. The several thousands of measurements that were logged during a 2 hour cool down period served as the basis for establishing the calibration curves. This procedure was repeated with several diluted samples in order to determine the correct relationship between the sound speed and concentration.

2 ON-LINE CONCENTRATION (RED LIQUOR MEASUREMENT) PAGE 2 OF 6 TEST RESULTS The graph below shows the relation between sound speed, temperature, and the concentration of red liquor. The graph above shows the relationship between sound speed and the concentration of three different temperatures. The polynomial algorithm that is built in the Model 8100 controller accurately determines the concentration out of any combination of speed and temperature data set. During all tests the sound speed was a steady signal, while the measured sound speed absorption, due to suspended solids, was constant for a specific concentration over the entire temperature range. The absorption is linear with the concentration of the diluted samples, thus making it possible to measure the amount of suspended solids separately, and direct this concentration available through the second analog output. ACCURACY The graph show an average sound speed slope of 3.6 m/s per WT% red liquor increase. This slope is considered good, making a reliable concentration measurement possible. The temperature slope is 2.7 m/s per C increase. This slope is considered good, and in fact it is better than is found with many other successful applications. The algorithm of the Model 8100 takes care of the temperature effect. The best accuracy of the Model 8100 under laboratory conditions is m/s and C. With these numbers, the calculated accuracy is WT%. However, it is assumed that the rough process conditions do not allow such a high accuracy. With an estimated average accuracy of m/s and C, the accuracy of the in-line analysis is 0.08 WT%.

3 ON-LINE CONCENTRATION (RED LIQUOR MEASUREMENT) PAGE 3 OF 6 MAINTENANCE The Rhosonics analyzer does not require any maintenance, since the reading is marginally affected by scaling. With the normal rinsing procedure, where hot water with some detergent is used, it is expected that the probe will be cleaned as well, therefore, fit for its purpose. The analyzer is equipped with the polynomial calibration for red liquor, as found in the factory. Should a small difference in reading between the instrument and the laboratory of the customer occur, an easy procedure is sufficient to correct the polynomial calibration. This procedure is only required after the initial installation and first test results. Once calibrated, there is no need to repeat the field calibration, as there are no components that can wear or drift with time. SUSPENDED SOLIDS MEASUREMENT The discussed analysis is primarily measuring the amount of dissolved solids. Eventual suspended solids have a negligible effect on the sound velocity. During the testing, it was noted that some amounts of suspended solids are present in the liquid. These solids do not have an affect on the absorption or attenuation of the ultrasonic signal. The attenuation is measured by the Model 8100 as well. Some additional testing is required to isolate the solids from the liquid in order to make various concentrations of suspended solids. Therefore, a second polynomial calibration can be programmed into the Model 8100 for the period of time that testing will occur in the customer s plant. For the trial period, the attenuation signal will be made available at the second output. This will enable the customer to evaluate the possibility of measuring suspended solids as well. In this way, there will be the ability to measure the real-time concentration of red liquor in the form of dissolved solids, at the same time as the concentration of the suspended solids. RED LIQUOR MONITOR Technical Features include: Measuring range: 40% to 60% Accuracy: % Product temperature: 120 C max. Product pressure: 10 bar max. On-line pipe: 2 inches lbs. Measuring cell type: PEEK Sensor: MCS-FTS-1-EX-2" 150 lbs (W-T-PEEK) Evaluation unit: Model 8100 or 8200 (1 or 2 channels) INSTALLATION IN PRODUCTION

4 ON-LINE CONCENTRATION (RED LIQUOR MEASUREMENT) PAGE 4 OF 6 CONCLUSIONS The Rhosonics Model 8100 is a reliable and accurate system that measures the concentration of the red liquor on-line. Under the least ideal process conditions (ie: strongly varying temperatures and varying composition of the red liquor), the accuracy of the sound speed is estimated at m/s, and the temperature accuracy is estimated at C. The resulting worst-case accuracy of the in-line analysis is then WT%. APPLICATIONS After and before digester (control of the cooking liquor to provide optimal digestion of the pulp - 0% to 15%) After washers - red liquor 12% to 20% solids After the multiple (affect evaporator - 10% to 20% and 50% to 70%) EXAMPLE OF SULFITE DIGESTER SONIC ANALYZER BEFORE AND AFTER THE DIGESTER LIQUOR CONTROL. THE CONCENTRATION OF THE COOKING LIQUOR PROVIDES OPTIMAL DIGESTION OF THE PULP.

5 7.10 ULTRASONIC ANALYZER ON-LINE CONCENTRATION (RED LIQUOR MEASUREMENT) PAGE 5 OF 6 MEASURING CELL (2" PIPE LBS) PROCON JANUARY 2004

6 7.10 ULTRASONIC ANALYZER ON-LINE CONCENTRATION (RED LIQUOR MEASUREMENT) PAGE 6 OF 6 SULFITE EVAPORATOR SYSTEM RHOSONICS MEASUREMENT OF THE RED LIQUOR DURING THE EVAPORATION PROCESS. THE CONCENTRATION IS MEASURED DIRECTLY ON-LINE WITHOUT CONTACT. RHOSONICS ANALYZER (MODEL 8100), MCS SENSOR PROBE (2") 150 LB CELL. MEASURING CELL WITH SENSOR PROCON JANUARY 2004