The use and maintenance of automatic calorimeter

The calorific value is a very necessary item for the analysis of coal quality, and it is the main quality index of coal used for power. According to its calorific value, the metamorphic degree of coal can be inferred to be an important parameter of coal classification index. The calorific value of coal has a significant contribution to coal production and sales.

From the aspect of coal detection instruments, the use of coal calorimeters has gone through three stages: the traditional Beckmann temperature calorimeter, the intelligent Chinese character semi-automatic calorimeter and the automatic calorimeter. Among them, the automatic calorimeter It has been promoted in the coal inspection system and it has been continuously updated to improve the efficiency of the work and the accuracy of the test results.

1. Structure and working principle of the automatic calorimeter 1. The structure calorimeter system of the automatic calorimeter consists of oxygen bomb, inner cylinder, outer cylinder, temperature sensor, stirrer, ignition device, temperature measurement and control system and water. . The host of an automatic calorimeter is generally composed of a casing, an outer cylinder, an inner cylinder, a backup water tank (or a fixed container), a stirrer, a temperature sensor, an ignition electrode, a water circulation system, and a control circuit.

Some automatic calorimeters also have an external cylinder temperature system and an external cylinder temperature control system that can maintain the temperature of the external cylinder and the temperature of the entire calorimeter system within a very small range, creating a relative balance for the entire calorimetric system. A stable measurement environment.

The working principle of 1,2 automatic calorimeter At present domestically produced calorimeter is mostly thermostatic. Its working principle is generally equipped with an oxygen bomb loaded with a sample of coal and oxygenated to a specified pressure into the inner cylinder subsystem to begin water circulation, stabilize the water temperature, and then inject water into the inner bobbin, and after reaching a predetermined amount of water, start stirring to make the inner cylinder temperature Equilibrate to room temperature (within a difference of 1.5°C). At this point, the temperature sensing head measures the water temperature and records it in the computer. When the water temperature in the inner bobbin is basically stable, the control system indicates that the ignition circuit is turned on. After ignition, the sample rapidly burns under the combustion of oxygen, and the heat generated is transmitted to the inner cylinder through the oxygen bomb, causing the water temperature of the inner cylinder to rise. When all the heat in the oxygen bomb is released, the temperature begins to drop. After the computer detects the drop in the water temperature of the inner cylinder, it is determined that the production, supply and sales test is completed, and the system stops stirring and releases the inner cylinder water. The computer processes the result of the collected temperature data.

However, some automated rapid calorimeters do not use the endpoint temperature of the test zone to calculate the calorific value. Instead, they use the pre-calibrated mathematical model to predict the endpoint temperature based on the temperature velocity during the primary phase. The data processing program in the software Calculate the calorific value and shorten the test cycle.

2. The use of automatic calorimeter 2. The new autocalorimeter needs to measure its heat capacity. The effective working range The automatic calorimeter has a high measurement speed and automation, but it may make the heat capacity of the calorimeter system change with temperature. Instead, the same heat capacity value cannot be used in all cases. The effective working range of the heat capacity shall be determined according to the method specified in GB/T213-1996, and the actual heat capacity value to be used under different test temperature rise shall be determined.

2、2 The heat capacity shall be re-calibrated in the following cases (1) The period of validity shall be 3 months (automatic calorimeter validity period shall be appropriate).

(2) Change the temperature control related authorities or temperature measurement card.

(3) Replace the calorimeter with larger parts (such as stirrers, oxygen bombs).

(4) Calibrate the heat capacity, determine the calorific value, and measure the calorific value. The difference between the water temperature of the inner cylinder and the inner cylinder is 5°C or more.

(5) The calorimeter is moved relatively.

(6) After replacing the external bobbin water.

(7) When checking the accuracy of the instrument with a reference material, if the difference between the measured value and the standard value exceeds the uncertainty range, or if the difference between the measured value and the standard value exceeds 50 J/G, the test value is not artificial or external. When caused.

Automatic calorimeter maintenance (1) often artificial water. The standard requires that the external cylinder water quantity be more than 5 times more than the internal cylinder water quantity, because the instrument will evaporate a part of water during idle time and during the test, and a part of water (about 2g each time) will be brought out when the oxygen bomb is removed during the test, and the lost water In the end, the water tank calorimeter will be reduced. As time passes, the outer tube will be short of water and the heat capacity will change. Some calorimeters will also reduce the amount of water in the inner cylinder, which will cause the inner cylinder to fail to meet the requirement of less than 1g per error. Therefore, depending on the size of the calorimeter, it is necessary to recharge the calorimeter from time to time.

(2) The accuracy of the instrument is often checked with standard coal samples. When the accuracy of the instrument deviates, it should be analyzed. If it is not a test operation problem, it should be immediately reheated. Check the accuracy of the instrument as far as possible without using benzoic acid, such as the use of benzoic acid should be as hot as possible so that benzoic acid should be as hot as possible so that the quality of benzoic acid is 0.7-0.8 grams, due to the temperature rise and heat capacity generated by 1 gram of benzene squaric acid Consistent, its temperature error detection is out.

(3) Control the ambient temperature. Theoretically speaking, the greater the difference between the water temperature of the outer cylinder and the ambient temperature, the greater the amount of heat exchange, and thus the greater the heat loss of the inner cartridge. Assuming that the heat capacity of the instrument is 10,000 J/K, the correction value will deviate. 0.01K, the heat will deviate from 100J/G, plus other factors, the calorific value will deviate even larger. From an experience point of view, the temperature of the outer cylinder will increase by 0.1 to 0.2 per one calorific value. If 10 samples are continuously made, the outer cylinder will have to rise. When the ambient temperature rises, the green manure will, according to experience, send the normal test value to the routine. It will be on the high side, so keep a good environment and ambient temperature, it is very important to ensure that the calorific test results show accuracy (4) regular replacement of external bobbin water. Water cartridges can be mixed with impurities for a long period of time, resulting in a change in the calorimetric heat capacity. Generally, the number of visual tests can be changed from 6 months to one year. However, if there is any dirt in the water, change the water immediately to avoid the normal operation of the water pump and the valve.

(5) After the end of each experiment, the calorimeter cover should be opened to accelerate the water temperature in the lower cylinder. If the calorimeter upper cover is not used for a long time, the inner cylinder is contaminated.

(6) Do not disassemble the instrument; do not start the pump when there is no water; intermittent use or standby instrument should always be powered on for waste sample test to prevent the valve and the pump from being inflexible or rust after long-term deactivation.

(7) Keep the inner cylinder clean. Ignition electrode should always be wiped to avoid surface fouling and cause ignition failure. The stirrer fan blade should be cleaned to prevent the deposition of the above-mentioned dirt and wash into the inner cylinder.

(8) Pay attention to protect the temperature probe and avoid collision. The probe is usually made of pure platinum wire wound on a glass rod. The surface is covered with a thin layer of glass. Once the glass is crushed, it will seep water, causing the resistance of the platinum resistor to change. At this time, the temperature display value will jump and the temperature measurement will not be accurate. At this time, the test should be stopped immediately, and maintenance and replacement should be carried out.

(9) Be careful not to spill the water on the edge of the inner tube during use to prevent the water in the inner and outer cylinders from being trapped in the water to cause a parallel sample to be out of tolerance.

(10) With Windows version of monitoring software, the computer cannot run other programs (including virus real-time monitoring program, screen saver, etc.) at the same time when testing, in order to avoid interference with the test process and affect the test results.

(11) Oxygen bombs should be subjected to a hydrostatic test of 20.0 MPa on a regular basis. After each hydrostatic test, the use time of the oxygen bomb should not exceed 2 years. Usually, attention should be paid to the structure related to the strength of the oxygen bomb, such as the connection between the cartridge and the connecting thread, the inlet valve, and the electrode and the oxygen warhead. If significant wear or looseness is found, it should be repaired and used after passing the hydrostatic test.