Continuous production processes involve the conversion tie raw materials or a combination of ingredients to achieve a final product. Being able to measure and control the physical and chemical properties of the ingredients of a product is essential to achieve a satisfactory quality of it. This is accomplished through instruments called analyzers.
Many of these devices, which in some cases require complicated sampling systems and special sensors, here we briefly discuss the measurement of only some physical and chemical properties.
DENSITY
The density of a material is its weight per unit volume. The simplest way to measure density of liquid is the hydrometer, which is a floating tool displaces a volume of liquid equal to its own weight. Usually constructed of glass and has a weight on one end to make it float upright. The position of the hydrometer into the liquid depends on the density of it. In some cases the measurement can be transmitted to a remote reading, using a metal rod as weight, which acts as an arm of a bridge variable inductance. Also measured fluid density, i weighing a fixed volume of fluid with a mechanical scale or load cell. Another method uses a slider-type meter. Here, the slider element is enclosed in a chamber of fixed volume. By changing the density, the force on the shifter varies, this in turn moves a balance, which is the actuating mechanism of a pneumatic or electrical measurement.
By using differential pressure transmitters for density measurement in either open or closed tanks, the hydrostatic pressure sensed a fixed volume is a function of density. The bubble method is also used to measure density. In some cases, the liquid does not allow the use of sensors due to corrosion, abrasion or other limitation, radioactive systems are adequate, a radioactive source is placed to one side and a detector reservorlo radioactive side. The amount of radiation absorbed by any material varies directly with density. The gas density measurement is important, especially in petrochemical industries. One way is to use a hydrometer with a probe. The device contains a membrane that varies with the passage of process fluid. Any variation in gas density causes the oscillation frequency also do it in reverse. The signal is then amplified and standardized in order to be transmitted.
ACIDITY AND ALKALINITY
The measurement of these variables is often of great importance in industrial processes. The measurement scale is called pH. This scale is based on the concentration of hydrogen ions in a volume of solution. In this, pure water has a value of 7. A strong acid has a value of 1 and a base (alkaline) the 14, with 7 being the value corresponding to pure water. Generally speaking, in practice the concentration of hydrogen ions for a given pH when it really refers to an "effective concentration".
PH measurement requires two electrodes designed specifically. One of them is a change in voltage (emf) when I change the pH of a solution in which it is immersed. The other electrode, maintains a constant voltage (emf) to be immersed in a reference solution. Usually, both elements are combined into a single electrode. As fluid temperature affects the measurement of pH, includes a temperature sensor for measuring system compensates for these changes.
You can find continuous pH analyzers in virtually any industry that uses water in its processes. Applications range from industrial water treatment to: control of pH in flotation processes for mining. Many applications of pH can be found in the pulp and paper, in the field of metals and metal treatment, the petroleum refining, manufacture of synthetic rubber, power generation plants, pharmaceutical, chemical and fertilizer production a wide spectrum in the chemical industry.
Figure 14 pH electrode
COMBUSTION
To properly monitor the combustion efficiency of a boiler, you should analyze the flow of gas before leaving the chimney. This including for air pollution control. The complete combustion products are also heat, carbon dioxide and water vapor. When sulfur in the fuel, sulfur dioxide is also a product of combustion. If carbon monoxide is detected, then that combustion is incomplete.
CHROMATOGRAPHY
Is the name given to the method of analysis that allows a continuous measure of the amount of each constituent in a complex vapor or gas mixture. The method involves the combination of a gas sample with a carrier gas and the combination of gases passing through a column, which is made of metal tubing and filled with an absorbent such as aluminum, silica gel or activated carbon. The effect of gas movement through the column is the separation of gas constituents of the sample, each component travels at different rates because each is held by a different time period for the absorbing column. The carrier gas, forcing the test to the spine emerges from the same continuum, such that the Framers actually leave the spine combined with the carrier gas, the most common are the ice carrier gases, nitrogen, air or hydrogen. A typical sample of gas may contain constituents such as ethane, propane, acetylene, butane, pentane and others.
ANALYSIS OF SOLID IN MINING
The mining industry based analyzers use X-ray fluorescence to analyze some elements in a flotation pulp. They are commonly analyzed elements such as chromium, manganese, iron, cobalt, copper, zinc and lead.
Figure 15 Team X-ray samples
As the primary source of radiation is X-ray tubes and sources of radioisotopes, although for reasons of environmental protection are preferred the former. Typically the system consists of (1) a sampling system that pumps the slurry to the analyzer, a spectrometer that measures ^ the elements of each sample, X-ray generator and a water cooling system. Modern systems also include a data processing equipment.
A continuous flow of sample is taken from each pulp process to be analyzed. The final sample flow is obtained after sampling at two or three stages depending on the amount of flow, of process. Each sample of pulp flows into a separate cell in the analyzer. The intensities of radiation measurements give all the information required to compute the actual contents. A timing device determines the measurement time for each sample of pulp.
The analysis or on-line monitoring of particle size (PSM) is another important operation in an ore concentrator plant for process control purposes. This is done in the crushing stage and is used for this purpose an ultrasonic sensor. There are two pairs of ultrasonic transducers, each with a transmitter and a receiver. At the transmitter, the high frequency electrical signals are converted into ultrasonic energy which travels through the flesh between the transmitter and receiver. At the receiver, this energy is converted back into high frequency signals and then treated for the purposes of being used as a standard signal instrumentation.
The amount of energy detected by the pulp comes in the form of two signals corresponding to the particle size and percent solids. The electronic comparison of these two signals gives an output that varies only according to particle size and is independent of changes in the percentage of particle.
