Emission Monitoring System

Transcription

1 Advance Cemas-FTIR Multi-component Emission Monitoring System System Description 30/ EN

2 System Overview Measurement principle The Advance Cemas FTIR is a multi-component emission monitoring system for simultaneously measuring HCl, HF, NH 3, CO, NO, NO 2, SO 2, H 2 O, CO 2, O 2 and organic carbon. The infra-red-active measurement components are measured at high temperature (180 C) using an FTIR spectrometer (FTIR = Fourier Transform Infra Red). The O 2 measurement is performed using an electrochemical oxygen sensor. The organic carbon content is measured using a flame ionization detector (FID); this is not a standard component of the measurement system. Mode of operation (see Fig. 1) The sample gas is piped via the heated sampling filter 2 and the heated sampling pipe 4 to the heated sample-gas feed 5. The heated cell of the FTIR spectrometer 11 protrudes directly into the heated sample-gas feed. Behind the gas outlet of the cell an FID 12 can be connected for measuring carbon within the sample-gas feed. A proportion of the sample gas stream is piped to the oxygen analyzer 13 from the heated sample-gas feed. Through the check valve 3 on the sampling filter 2 dry compressed air is released automatically in the event of any problem, e.g. if the temperature falls below the permitted level in one of the heating circuits. The system is also purged of sample gas to avoid condensation. Through the second check valve 10 dry, CO 2 -free compressed air is automatically released for the purpose of recording zero-gas spectra. The molecular sieve unit 14 is used for conditioning the compressed air, i.e. drying it and reducing its CO 2 content. Fig. 1 Diagram of pneumatic system (Optional) C analyzer FTIR spectrometer Purging (Optional) O2 analyzer >1% >1% Waste gas 5 Meas. cell Waste gas l/h Purging gas Compressed-air purificationunit withco 2 separator Compressed air kpa (6...8 bar) 14 Test gas 2 Advance Cemas-FTIR System Description 30/ EN

3 Sampling system F In this section the reference numbers printed in italic refer to Fig. 1. Sampling system The sampling system comprises: the probe tube the filter device and the sampling pipe Probe tube The probe tube 1 is made from special steel (1.4571) and can be supplied in either an unheated (probe 40) or a heated version (probe 42) and in lengths 1 m, 1.5 m and 2 m. A heated probe tube is only necessary in exceptional cases (e.g. cold bridge on the flange). Filter device The PFE2 filter device 2 contains a coarse filter (20 µm) that is heated to 180 C. The sampling pipe is connected directly to the filter device. For emergency purging of the entire sample-gas path from the inlet via the sample cell up to the outlet, cleaned compressed air is released through a heated check valve 3 on the filter device. For external installation of the sampling probe an optional protective probe case can be supplied. For situations with a high dust content a purging facility can be supplied for periodic cleaning of the coarse filter. Sampling pipe The sampling pipe 4 can be heated to 180 C by a built-in fixed-resistance thermistor (90 W/m). The temperature is monitored using a Pt-100 sensor. The sample gas is transported in a PTFE hose (8 x 6 x 1 mm). In order to avoid a long dead time the sampling pipe should be no longer than 40 m. 30/ EN Advance Cemas-FTIR System Description 3

4 Feeding and conditioning of sample gas F In this section the reference numbers printed in italic refer to Fig. 1. Sample-gas feed The sample-gas feed comprises: the needle valve, the sample-gas feed pump, the fine filter, the flow monitor and the check valve for releasing zero gas and test gas. The sample-gas feed is housed in a warming cabinet. Needle valve The needle valve 6 is used for adjusting the sample-gas flow during commissioning of the measuring system. Sample-gas feed pump The motor for the sample-gas feed pump 7 is attached on rubber mounts to the right-hand side panel of the warming cabinet. The whole top of the diaphragm pump protrudes into the warming cabinet. Fine filter The ceramic fine filter 8 serves to separate out the finest particles. It has an average porosity of 0.05 µm. Flow monitor The flow monitor 9 is based on a Reed contact with a magnetic piston seated in PTFE. The lower switching point is set to 250 l/h. If flow falls below this rate the status signal Fault is output. Check valve Through a check valve 10 between the pump and the fine filter both zero gas and test gas can be released. This valve is controlled by an external magnetic valve. An opening pressure of 700 hpa (= 0.7 bar) is required. Warming cabinet The warming cabinet is heated to 180 C to prevent the temperature from falling below the dew point. Temperature control is handled by an external temperature controller with a Pt-100 temperature sensor in the warming cabinet. For connecting the heated pipes, mounting flanges are fitted on the left and right side panels of the warming cabinet in such a way that no cold bridge can develop. The internal piping in the sample-gas feed is in 6 x 4 x 1 mm PTFE. Transition pieces are made from special steel as Swagelok connections. 4 Advance Cemas-FTIR System Description 30/ EN

5 FTIR spectrometer FTIR spectrometer (see Fig. 2) The FTIR spectrometer, model MB9100, is installed suspended in the system cabinet. Its main components are as follows: the interferometer with the electronics for controlling the spectrometer and communicating with an external computer 1, the IR-ray source 2, the transfer optics and the IR detector 3 and the cell 4. Fig. 2 FTIR spectrometer Interferometer The interferometer modulates the IR light along with the light from the laser and from the white-light source. The latter two are used for scaling the spectrum. The complete interferometer unit comprises the above light sources, their power supplies, the detectors for laser light and white light, the beam splitter, the retroreflectors, the transfer mirrors and the interferometer arm. The interferometer arm is distinguished by its twin-pendulum design which contributes to the spectrometer s robustness and freedom from oversensitivity. Continued on next page 30/ EN Advance Cemas-FTIR System Description 5

6 FTIR spectrometer, continued IR-radiation source The source of the IR radiation is a glowbar, a resistor with positive temperature characteristics, made from silicon carbide. IR detector The IR detector is a DTGS detector (deuterized triglyceride sulfate). Cell Connected to the spectrometer is the heated long-path cell. Via an optical transfer device located above the cell the IR ray passes into the cell. In the cell it is reflected several times by three mirrors for increasing the length of the optical path before leaving the cell again and arriving at the detector. The optical path length is fixed in the factory through the setting of the mirrors. It is normally 6.4 m. Processing of measured values The digitized detector signal is evaluated in terms of concentration of the different sample-gas components by a computer that forms one of the system components. 6 Advance Cemas-FTIR System Description 30/ EN

7 Oxygen analyzer Sample-gas feed A proportion of the sample gas stream is diverted and piped to the oxygen analyzer from the sample-gas feed. To prevent condensation the sample gas is passed along the heated cell and into the oxygen analyzer. Oxygen sensor The type KE-25 electrochemical oxygen sensor in the oxygen analyzer operates on the same principle as a lead acid battery. The cathode of the electrochemical cell is made of gold and the anode of lead. A weak acid is used as an electrolyte. At the cathode the oxygen entering from the sample gas is absorbed electrochemically, a process through which electrons are used up. At the anode lead releases electrons and is oxidized to form lead oxide. The current flowing through the outer circuit in this process is proportional to the diffusing oxygen. The diffusion from the gas phase is limited by a porous barrier so that a linear signal results corresponding to the concentration of oxygen. The surface of the lead anode regenerates itself continuously as the lead oxide dissolves in the electrolyte. Removal of condensate In order to remove the condensate the sample gas is passed over a condensate trap. The condensate is expelled from the filter housing by means of a peristaltic pump. Flow monitoring Monitoring the flow upstream of the oxygen sensor ensures a minimum flow of 10 l/h. If the flow rate falls below this value, then a status signal Fault is output. Discharge of the condensation heat The condensation heat is discharged through the cooling device in the system cabinet. For this purpose a cold-air pipe passes from the cooling device into the oxygen analyzer. Processing of measured values The analog sensor signal is digitized, incorporated into the processing of measured values from the Advance Cemas FTIR, and displayed on the screen. The measured value for oxygen, in common with all other measured values, relates to the moist flue gas. Adjustment The oxygen analyzer is automatically adjusted during the daily recording of the zero spectrum. 30/ EN Advance Cemas-FTIR System Description 7

8 System design System cabinet (see Fig. 3) All components of the system are housed in a system cabinet. In the upper, cooled section are the FTIR spectrometer 1, computer 2, control system and analog outputs 3, temperature controller 4 and as an option the O 2 analyzer 5 (not shown in Fig. 3). Located in the lower section of the cabinet is the heated sample-gas feed 6. Fig. 3 System design Control and monitoring of temperature All the heated circuits, i.e. filter system, sample-gas pipe, sample-gas feed and sample cell in the FTIR spectrometer are regulated and monitored to 180 C. If the temperature falls below this level a Fault status signal is output and the complete sample-gas path is purged with dry air via the filter apparatus. Operation, display and data output During commissioning, shutting down or maintenance tasks the system is operated via a menu-driven user interface displayed on a PC monitor. A PC keyboard enables operations to be controlled, parameters to be set and the menu to be modified. All measured data are displayed on the screen in the units requested, and also output in the form of analog signals (4 20 ma). All measured values relate to moist sample gas. Subject to technical changes Printed in the Fed. Rep. of Germany 30/ EN 02.97