Coal calorific value tester, fully automatic calorimeter, calorific value machine

Coal calorific value tester, fully automatic calorimeter, calorific value machine

Coal calorific value tester, fully automatic calorimeter, calorific value machine

The calorific value is an important indicator for evaluating coal quality. As the main parameter for calculating the economic indicators of thermal power plants and the main basis for coal pricing, as well as a necessary condition for stable combustion of boilers, the detection and application of calorific value play a very important role in thermal power plants.

The impact of accuracy of measurement results and solutions

01

The impact of environmental temperature

The experiment should be conducted in a separate laboratory at room temperature not exceeding15～30℃If the temperature is too low, the reliability of the experimental results will be greatly affected. In order to maintain room temperature, many laboratories install air conditioning. It should be noted that the air conditioning outlet cannot directly face the calorimeter, and measurements can only be taken after the room temperature has stabilized. The temperature difference between the water temperature in the outer barrel and the room temperature shall be adjusted within half an hour after the general air conditioner is turned on1.5KCalorimetry measurement can only be conducted within the specified range. National standard requirement: every change in ambient temperature5℃The heat capacity should be recalibrated.

02

The impact of thermal capacity calibration

The key to the accuracy of heat generation measurement lies in the accuracy that can be achieved by calibrating the heat capacity, as well as the consistency between the heat capacity calibration conditions and the heat generation measurement conditions. The close agreement between the repeatability test results does not necessarily mean that the results are accurate, and they may include systematic errors caused by inaccurate heat capacity. The calibration of thermal capacity must strictly use second level or above reference calorimeters that have been verified by the metrology department and have been marked with their calorific valueBenzoic acid is used for calibration. When benzoic acid burns in an oxygen bomb, a portion of the nitrogen remaining in the bomb will generate nitric acid, which will release heat during the reaction. Therefore, when calibrating the instrument's heat capacity, the heat of nitric acid formation should be added to the total heat released in the oxygen bomb, while the accuracy of the instrument should be subtracted from the heat of nitric acid formation. Benzoic acid should be finely ground in advance and dried in a dryer containing concentrated sulfuric acid3dor60～70℃Drying in an oven3～4h,After cooling, the tablets are compressed, and the quality of the tablets is determined by0.9～1.1gIt is appropriate. The calibration of thermal capacity should generally be carried out5The relative standard deviation of repeated experiments should not exceed0.20%If it exceeds0.20%Conduct another experiment and select those that meet the requirements5The average value of the secondary results is taken as the thermal capacity of the instrument. If any5The relative standard deviation of the secondary results exceeds0.20%After carefully checking and correcting any issues with the experimental conditions and operating techniques, recalibration should be carried out and all existing results should be discarded. What is the validity period of thermal capacity calibration3Month after month, when replacing the calorimeter, major components of the calorimeter, calibrating the heat capacity, and measuring the temperature difference of the inner cylinder during heat generation5℃When the calorimeter needs to be moved significantly, the thermal capacity of the instrument needs to be recalibrated.

03

The influence of inner cylinder water volume

The amount of water in the inner cylinder is the biggest factor affecting the accuracy of the measurement results. The heat capacity of the inner cylinder water accounts for a considerable proportion of the total heat capacity of the instrument. Due to the high specific heat of water, inaccurate water content in the inner cylinder will cause changes in the instrument's heat capacity, leading to measurement errors in heat generation. The water in the inner cylinder of the automatic calorimeter enters the inner cylinder through a fixed container. If the water quality cannot be guaranteed or the water volume cannot be kept consistent, it will increase the deviation of the measurement results. Therefore, it is necessary to pay attention to checking whether the solenoid valve of the calorimeter is blocked and whether the magnetic pump is working properly. Once the ignition wire or other residue is found to block the solenoid valve, it should be cleaned in a timely manner. The filter screen of the inner cylinder should be cleaned every day, and the dirt on the inner cylinder wall should be wiped with clean gauze or gauze dipped in alcohol to keep the inner cylinder wall clean. If there are flocculent floating objects on the filter screen of the inner cylinder, the water should be changed and the thermal capacity of the instrument should be recalibrated. Regularly add water to the instrument, as some water is brought out during each experiment and a portion evaporates every day, causing the water in the calorimeter to decrease. Regularly adding water to the instrument can make it work more stably.

04

The influence of coal samples and weighing methods

right0.2mmThe particle size requirement for coal samples is that they can all pass through the pore size of0.2mmUse a sieve and wait for the coal sample to reach a state of air drying before putting it into a bottle and mixing the coal sample evenly. To ensure the accuracy of heat generation measurement, it is necessary to first ensure that the coal sample being weighed is representative. Therefore, it is required that the laboratory personnel shake the coal sample thoroughly using the rotary bottle method before weighing, and then use the multi-point weighing method at different parts to weigh the coal sample. Then, the loose coal sample obtained from the weighing should be compacted to prevent the coal sample from splashing and causing incomplete combustion, resulting in a lower heat generation measurement value.

05

The influence of combustion dishes on the determination of calorific value

(1)If the newly purchased combustion dish is directly measured without treatment, there will be a phenomenon of low heat generation results. In order to avoid this situation, the combustion dish needs to be tested before use800℃Burn it in a high-temperature furnace until it reaches a constant weight before conducting the measurement.

(2)The thickness and depth of the combustion vessels produced by different manufacturers are not the same, so the quality is also different. Even if a combustion vessel is produced by one manufacturer, the quality may sometimes be different. Experimental results have shown that the calorific value of a light and thin combustion vessel is greater than that of a heavy and thick combustion vessel. Therefore, in the precise determination of heat generation or calibration of heat capacity, it is recommended to use combustion dishes with relatively consistent quality as much as possible. The walls of the combustion vessel should not be too high, and the bottom should not be too thick. The bottom of the combustion vessel should have a clear curvature to avoid forming blind spots.

06

The Influence of Coal Sample Combustion Stability

After the measurement of calorific value is completed, incomplete combustion is prone to occur due to various reasons, such as coarse coal sample, poor coal quality, insufficient oxygen filling pressure or oxygen bomb leakage, low oxygen pressure, and deep burial of ignition wire in coal powder. Different measures should be taken according to different situations. A coal sample that is too coarse may result in incomplete combustion. In this case, an agate mortar can be used to grind the coal sample fine; For coal samples with low volatile matter and high ash content, a layer can be placed at the bottom of the combustion vessel800℃Test the calorific value of burnt asbestos wool by wrapping it with mirror paper or paper mixed with benzoic acid; For high volatile coal samples, a slight contact between the ignition wire and the surface of the coal sample is sufficient. Cut the coal powder into pressed cakes2～4 m mUse small pieces. The oxygenation time should be relatively consistent and basically controlled within30～45swithin,If the oxygen pressure of the oxygen cylinder is lower than5MPaNew oxygen should be replaced. If the oxygen pressure in the oxygen bomb exceeds3MPaThe oxygen inside the oxygen bomb should be exhausted, the bomb should be reinstalled, and oxygen should be refilled. Before the daily experiment, the oxygen bomb should be filled with oxygen and placed in water to check its airtightness. If no bubbles appear in the oxygen bomb, it indicates good airtightness. If bubbles appear, the cause should be promptly identified and treated before use.

07

Other influencing factors and measures

In the determination of coal calorific value, in order to reduce experimental errors, a coal standard sample should be taken before each formal measurement of the coal sample. The formal measurement can only be carried out when the measured value of the standard sample falls within the uncertainty range of the standard value. The oxygenation time should be relatively consistent to avoid the phenomenon of low results caused by insufficient oxygenation time leading to incomplete combustion of coal samples. The amount of distilled water added to the oxygen bomb must be ensured10ML, if more water is added, the heat absorption will increase, and the test results will be lower. After each test, all components of the oxygen bomb should be cleaned and wiped dry. The water used to clean the oxygen bomb should be close to room temperature to avoid a large difference between the temperature of the oxygen bomb and the water temperature in the constant temperature bucket, which may affect the results of the next test. The combustion dish should be placed on an electric furnace to dry and cool before use.

In summary,In the process of measuring coal calorific value, the testing personnel must strictly follow the national standard operation, correctly handle the problems encountered in the work, timely eliminate faults, and ensure that the measurement results are accurate, reliable, and error free.