Measure Gas Temperature.pdf

Measure gas temperature by thermocouple Pyroprocessing Grinding

PROCESS MEASUREMENT TECHNIQUES - PR PMT P08-04 V1.0

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Introduction ƒ Gas temperature (dry-bulb) is one of the key elements used in analysing plant stability and performance. ƒ Measurement of gas temperature technique must be conducted in a correct manner to obtain accurate results

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This procedure explains how to measure gas temperature using thermocouple. A thermocouple is inserted into gas duct upstream to measure gas temperature. Measuring port must be plugged up to avoid leaked air into gas stream. The measurement is normally conducted by Process Technicians and Engineers.

Gas Flow

162 oC

Leak air

Safety aspects ƒ Depending upon the measurement location the operators have to be aware of a possible high temperature and take care of possible variations of pressure.

ƒ Only measurement points with safe access platforms are to be used. ƒ Be careful when opening measuring points, particularly if under positive pressure, avoid standing directly inline with an open socket.

ƒ Personal safety equipment is compulsory.

Prerequisites The measurement of gas temperature is quite straight forward but several prerequisite are required before doing the measurement:

ƒ Determine the purposes of performing the gas temperature measurement. ƒ Cross checking the accuracy of real time temperature in PLC ƒ Calculation of gas density for gas flow measurement ƒ Calculation of gas enthalpy” ƒ Good knowledge of Plant Safety Procedures to ensure safe working environment. ƒ Good knowledge of Plant safety interlocking is important in order to avoid any interference with plant operations. All rights of reproduction, representation, adaptation and translation relating to this report belong to Lafarge SA. Lafarge SA reserves the right to exploit this report or not and to freely distribute it to all of its current and future subsidiaries worldwide in any form, whether paper, electronic or digital, including via internet and/or intranet. This report along with its content is of a confidential nature. In particular, it may not be reproduced, copied, transmitted, published, divulged and/or appropriated in whole or in part for personal use or for use by a third party without prior consent from the Production & Process Department, except for reproduction by or for affiliated Lafarge companies.

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Measure gas temperature by thermocouple Pyroprocessing Grinding

PROCESS MEASUREMENT TECHNIQUES - PR PMT P08-04 V1.0

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ƒ Knowledge of location of measuring points is certainly important when doing gas temperature measurement.

ƒ For cross checking purposes, ensure that separate measuring holes at same location are available. This is to avoid interference to plant computer process control (interlockings).

ƒ For air flow and enthalpy calculation purposes, gas temperature measurement is always done together with gas flow measurement at the same measuring points.

1 How to measure gas flow by Pitot tube ƒ Special attention must be paid when measuring gas temperature at: ƒ Pre-calciner vessel ƒ Close to distribution box ƒ Cooler inlet (secondary air) ƒ Close to fresh air damper ƒ Knowledge about duct cross sectional area. It is important to know the duct diameter to determine the length of thermocouple to be inserted

ƒ In very dusty environment, it is important to get thermocouple with higher sensitivity which can read and stabilise faster. This is because thermocouple might be easily coated and might give inaccurate reading. A fine couple with 1.6 mm to 3 mm thickness can be used to measure real instantaneous temperature. A larger size couple with 5 to 6 mm thickness can be used to measure temperature which required smoothing of variations.

Time frame ƒ Recording of gas temperature over a period of time when the system is stable. ƒ It is useful to make redundant measurements for cross checking purposes ƒ Cross check with CCR operators for confirmation as well.

Tools ƒ Certified K type thermocouple – select thermocouple which has been calibrated and certified fit for use ƒ Certified Electronic thermometer – select electronic thermometer which has been calibrated and certified fit for use. Also use thermometer which can support the type of thermocouple you use.

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Adjustable spanners to open port holes. Cloth or rubber to plug the port when doing measurement. Hand Gloves to handle hot objects Safety Goggle to protect from spurting hot gas. Helmet as basic safety working gear. Protective clothing to protect from spurting hot gas and hot objects. Walkie – talkies for communication with CCR operators. Small notebook to record measurements.

All rights of reproduction, representation, adaptation and translation relating to this report belong to Lafarge SA. Lafarge SA reserves the right to exploit this report or not and to freely distribute it to all of its current and future subsidiaries worldwide in any form, whether paper, electronic or digital, including via internet and/or intranet. This report along with its content is of a confidential nature. In particular, it may not be reproduced, copied, transmitted, published, divulged and/or appropriated in whole or in part for personal use or for use by a third party without prior consent from the Production & Process Department, except for reproduction by or for affiliated Lafarge companies.

Procedure Template developed by

Measure gas temperature by thermocouple Pyroprocessing Grinding

PROCESS MEASUREMENT TECHNIQUES - PR PMT P08-04 V1.0

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Action Steps 1

Determine location for measuring points ƒ Determine the exact and suitable location of gas temperature measurements.

Location of gas temp measurements

ƒ Special attention must be paid when measuring gas temperature at: ƒ Precalciner vessel (several sets of measuring points are required to map the temperature) ƒ Close to distribution box (raw meal can affect the gas temperature) ƒ Cooler inlet for secondary air (several sets of measurements are required to map the secondary air temperature)

ƒ Close to fresh air damper (beware of false air in-leakage that can affect the gas temperature)

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Prepare the measurement points This step is closely associated with the procedure "How to measure gas flow by Pitot Tube”.

ƒ Holes will be drilled according to the dimensions of the Pitot tube. In round ducts, generally at least 2 holes are necessary in order to get a precise mapping of the gas flow and temperature. In the case of rectangular the number will be greater.

ƒ Ideally the location of the sampling points for flow and gas temperature measurement should be in a straight section of 5 pipe diameters before the measuring point and 2 diameters afterwards, to ensure a stabilised velocity and temperature profile. However, this is not always possible and measurements need to be taken in the section of ductwork that most closely matches this criterion.

ƒ Normally a vertical duct is chosen to make the measurements, particularly when dust is present in the gas stream, in case of settlement on the bottom. In the case of very moist gases containing dust, such as mill or dryer exhaust ducts check for any signs of dust accumulation, even on vertical ducts.

ƒ Measure the flow and temperature after de-dusting when possible (measure better after a cyclone than before) and, for instance, estimate the air in-leaks by oxygen measurements when possible.

ƒ Check in advance of the measurements that the sockets for the measuring points can be opened easily. ƒ In there is any uncertainty about the duct cross section, use a straight steel rod to check its dimensions. ƒ For gas temperature measurement with cross checking purpose, the measuring point hole can be drilled beside the existing point.

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Prepare the thermocouple and electronic thermometer. ƒ Ensure that the correct type of thermocouple and electronic thermometer are used. ƒ Also ensure that the cable between probe and thermometer is long enough to ensure smooth and safe measuring.

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Measure gas temperature by thermocouple Pyroprocessing Grinding

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Measure the gas temperature Before starting, always ensure all SAFETY PRECAUTIONS have been undertaken. Always inform CCR personnel before performing measurements. Keep very close contact with the CCR operator.

ƒ Determine the direction of gas flow. ƒ When introducing the thermocouple in a very dusty and wet gas environment, use a thermocouple which can read and stabilise quickly in order to avoid inaccurate measurements due to coating formation on thermocouple probe.

ƒ Set up the thermocouple and electronic thermometer. Ensure the thermocouple terminal block is connected into the correct terminal of electronic thermometer.

ƒ Prepare the thermocouple with cloth or rubber seal wrapped around the thermocouple probe. ƒ Open the port hole plug or steel plate cover with adjusted spanner and hand gloves. Do not stand in line with the port hole when opening the plug or steel plates.

ƒ Insert the thermocouple probe into gas upstream and seal the hole with the cloth or rubber. ƒ Wait for the temperature to stabilise and then record the measurement on a notebook. ƒ During the measurement, observe the evolution of the readings along the time on each point, a drift can be an indication of a progressive dust coating formation on thermocouple or high cool air in-leakage or serious gas stratification inside the gas duct due to plant instability. In such case, corrective steps must be taken to avoid serious error in measurement:

ƒ Check with CCR operator to confirm the stability of the plant. ƒ Clean the thermocouple probe. ƒ Check for in-leakage and eliminate the in-leakage. ƒ

The validity of the temperature profile can be checked by comparing the measurements taken at the same point on the inwards and the outwards profile.

ƒ It is advisable to perform several set of temperature readings to minimize the calculation errors.

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