A block diagram of a typical system is seen in figure 3. The analyzer has the capability of controlling the automatic switching valve as well as performing the calculations to determine HCl and Cl2 concentrations.
Field Experience and Applications
The chiller technique been successfully used to monitor ambient air levels of chlorine near a town located within 25 miles of a major chlorine producer. The analyzer has a range of 0-500 ppb, and is located in a remote monitoring station were it runs unattended except for weekly inspections. The system has run for nearly 2 years without problems. Typical levels measured were less than 20 ppb, and no interference has been noted from HCl or other gases.
IMS has also been successfully used in monitoring for HCl and Cl2 emissions from the combustion of rocket fuel at the low ppb level, with good agreement with standard wet methods. PPB and low ppm level analyzers have been used in applications as diverse as ambient air monitoring in chemical and plastic manufacturing plants, for testing wet scrubber efficiency and for monitoring Cl2 levels in corrosion test chambers. In many cases, IMS was the only technique with sufficient sensitivity, accuracy and specificity to make the required real time measurements.
A number of stack applications have been addressed with IMS analyzers as well. PPM levels of HCl have been monitored in hazardous waste incinerators and in stacks associated with pigment production. Cl2 has been monitored at the ppm level in stacks associated with TiO2 manufacturing, precious metal recovery, crematoriums, vinyl chloride production, and a wide variety of other industries. The IMS systems have performed well in these demanding applications, were other techniques have either failed or were not usable. At a number of locations, the analyzers are required by state or local regulations. As such, they are subject to the same quality control specifications as other Continuous Emission Monitors for accuracy, stability and reliability. Very good performance has been noted in zero and span drift tests, as well as quarterly calibration gas audits.
