A worldwide supplier of precision-machined industrial graphite components provides parts in a variety of shapes and sizes for use in multiple industries, including mining, aerospace, transportation and power generation. Components are formed by impregnating carbon with various solvents, catalysts and resins.

The formed products are loaded onto racks, which are then rolled into a flash-off room where they sit for a time to allow the solvents to flash off at room temperature. The racks are then placed in batch ovens to cure.

Cause for Concern

The company had a plant safety audit done and it was discovered that there was nothing on the ovens to protect against explosions. Initially, the company did not think it needed added protection, as its batch ovens were designed for maximum load conditions. The company used its own calculations to determine the batch load depending on the product type.

However, a batch of brushes was loaded into an oven without giving them time to flash off, and the plant had an explosion. The company realized it needed to take steps to avoid similar situations in the future.

Finding a Solution

A number of requirements led the company to the selection of the PrevEx analyzer for its operation. The oven atmosphere contained many different solvents and other materials such as resins. It required an analyzer that, when calibrated, would remain accurate for all constituents in the sample. The analyzer also had to run at a temperature high enough to keep all the oven atmosphere elements in the vapor state. In addition, the company also wanted to be able to integrate the analyzer into its existing process oven control system.

Based on these criteria, the company purchased a PrevEx SNR675 analyzer. The industrial-strength SNR675 assembly consists of a heated flame cell and an integrated controller that continuously measures total flammable vapor concentrations from 0-100% of the lower flammable limit (LFL) range. (Optional modifications allow the SNR675 to sample low oxygen and inert atmospheres.)

Proprietary flame temperature technology ensures an accurate and linear response. A carefully metered pilot flame incinerates the sample; the resulting change in flame characteristics is proportional to the total concentration of flammable vapors present.

To avoid condensation during sampling, the entire analyzer assembly is heated to 270°C (518°F), eliminating inaccurate readings caused by solvent dropout and excessive maintenance time due to sample condensation and clogging. A concentric sampling probe further ensures accurate, trouble-free sampling. Suitable for monitoring many common solvent vapors, the analyzer is unaffected by the temperature of the process and can sample streams above 1,500°F.

The assembly mounts directly onto the process ductwork (as close as possible to the sample pickup point), which eliminates external heated sample lines and allows the fastest response time. The analyzer employs customer-supplied compressed air to drive its integrated air-aspirated sampling system. This method is simple, has no moving parts and requires very little maintenance. The sampling system does not require bottled air or sample pumps. Auto-calibration solenoids are standard, enabling the remote activation of calibration tests.

A fault relay de-energizes whenever any of the following occur: controller electrical failure, loss of system power, loss of heat, loss of flow through the flame cell, or downscale readings caused by loss of flame or fuel. The system includes six relays: single-pole, double-throw relays for Warning, Danger and Fault; and single-pole, single-throw relays for Horn, Calibration-in-Progress and Service Needed. Other standard outputs include a 4-20 mA analog output and an RS-485 serial port with Modbus protocol. Digital remote access and control is made possible with optional operator interface panels.

The detector’s response time is less than 1 second. In addition, the analyzer exhibits a very stable zero (less than 1% drift in 30 days), and calibration accuracy has less than 5% error per year.

Enjoying the Results

Right after the company installed the SNR675, it was shocked to find that the ovens were experiencing much higher LFL levels than original design calculations showed. The company ordered 11 analyzers to be put on the remaining ovens as soon as possible to protect product, ovens and personnel.

With the installation of the PrevEx analyzers, not only is the company safer, but it is also seeing trends and data that can help it better utilize its ovens. “Initially installed to improve safety, now we have a tool that can be used to improve our process.”

 For more information, visit www.controlinstruments.com.