A new pressure transmitter with a specially coated diagram directly measures pressures of pulverized coal, eliminating long sensing lines. Conventional installations involve sensing lines as long as 30 to 50 feet to transfer the sensed pressure (about 30 to 40 inch WC) to a rack of transmitters. The long impulse lines are a maintenance headache, and often become plugged.
A small air purge in the sensing lines provided positive pressure in an attempt to keep the coal out of the sensing line. Despite this, wet coal resulted in frequent plugging problems, especially during the long winter months or from seasonal rains. In the worst cases, maintenance technicians have to drill out impulse lines plugged with dried "mud."
The pulverized coal comes from a Raymond Bowl mill. A certain "sweet spot" of pressure indicates smooth and proper operation of the mill, as well as the piping that takes the pulverized coal to the boiler furnace. If the pressure drops, the mill could be plugged or the fuel supply cut short. Conversely, a higher than normal pressure may indicate plugging of downstream coal ducts leading to the furnace. Improper pressures often lead to flame instability, productivity losses, and pollution.
To eliminate costly maintenance and burner inefficiencies, the plant installed the ABB 2600T series pressure transmitter with a direct mount seal. This transmitter was specified with a six-inch extension to give the measuring diaphragm a 3/4-inch set-back from the interior surface. The diaphragm has a patented Diaflex™ coating that withstands harsh environments.
Diaflex, with hardness similar to a diamond, is a nano-structured material with anti-abrasion physical characteristics. Constituents of the coating are titanium and silicon (SiTiN) of the nitrides class. Using a process called Physical Vapor Deposition (PVD), ABB coats the 316L Stainless Steel diaphragm seal to a thickness ranging from 3 to 5 µm, which provides good sensitivity to the pressure, while maintaining a Rockwell Hardness of 4000 HV in a nominal flow rate of 162 ft / minute.
After eight months, inspection of the diaphragm seal at the power plant showed no visible damage.
ABB is a leader in power and automation technologies that enable utility and industry customers to improve their performance while lowering environmental impact. The ABB Group of companies operates in around 100 countries and employs about 107,000 people.
SOURCE: ABB Measurement & Analytics