In fluid sensing applications, accurate pressure readings are essential to the process. A pressure device that offers long-term stability and reliable status indication contributes to insuring a smooth running operation.
In the case of FMC BioPolymer Corp, based in Newark, DE, pressure detection was put to the test in a chemical manufacturing facility running 24 hours, seven days a week.
FMC BioPolymer Corp markets products, systems, and services to the pharmaceutical and food ingredients industries, and is a leading producer of functional excipients, such as microcrystalline cellulose (MCC).
MCC is a white, odorless, tasteless powder that is used as a binder in prescription medications and is included in over-the-counter pain relievers and cough/cold remedies. The product acts as a stabilizer and thickener that can replace fat and absorb moisture in food products such as frozen desserts, salad dressings, nonfat yogurt, and pie fillings.
MCC and other cellulose-based products manufactured by FMC are derived from purified wood pulp. To transform paper-thin sheets of raw wood pulp into a fine microcrystalline cellulose powder, FMC uses a network of applications, one of which is found in the slurry processing area. FMC''s slurry application encompasses a series of vessels and transfer pumps that process the product. The end result is a fine powder, ready to be used in medicines and food products.
Inherently difficult to handle, slurry can present pressure sensing challenges. To travel to each vessel, the medium moves through transfer pumps and pipes in the system. Maintaining proper pressure in the transfer pumps is vital to the process. To detect pressure throughout the application, FMC was using pressure isolators or "pressure donuts," as they were referred to on the plant floor. A pressure isolator is a section of pipe containing an elastomeric bladder that holds a fill fluid. The isolator''s elastomer element or diaphragm is the same diameter as the pipe, allowing a seamless integration into the pipe. The medium travels through the pressure isolator, exerting pressure on its diaphragm. As the diaphragm flexes, it transmits pressure via the fill fluid up to the isolator''s controlling instrument, such as a gauge, switch, or transmitter. In theory, pressure isolators are sufficient for monitoring slurries.
However, challenges were encountered with isolator installation. A section of pipe is cut and fitted with two flange adapters on either end of the pipe opening. The pressure isolator is then inserted between the two flanges, which are tightened to make a clean seal.
FMC found that damage was occurring to the rubber elastomer after the flange adapters were tightened. Pressure from the flanges would pierce the elastomer, creating a tiny hole in the diaphragm. During setup, if the isolator read "no pressure," FMC''s maintenance personnel would stop the line, remove the flanges and examine the isolator.
At times, "no pressure" readings occurred for other reasons. A rupture in the diaphragm or trapped air in the fill fluid prevented the fluid from transmitting the proper line pressure. The combination of rubber elastomer and slurry also proved problematic: if a crevasse developed in the elastomer, medium could stick in the crevasse and harden, creating a possible contamination condition. To correct these problems, the isolator would be returned to the factory for maintenance, or completely replaced.
FMC''s electrical and instrumentation engineer, Jerry Daniels, began looking for a solution to his failing pressure isolators. "When there''s a 50/50 chance the isolator might fail, and someone had to stand at the pump constantly checking the status, I lost confidence in the product," stated Jerry.
He found a solution in ifm efector''s flush mount pressure sensors. FMC replaced the pressure isolators with ifm efector''s PF Series pressure sensors. PF Series sensors provide a 4-20 mA analog and switched output in a compact 316 stainless steel housing. Incorporating the same ceramic pressure sensing technology found in high accuracy pressure transmitters, the sensor provides high burst pressure and overpressure protection. The sensor''s compact housing incorporates flexible film technology that results in excellent shock and vibration resistance.
The first advantage over the pressure isolators was easy installation. A hole is drilled into the top of the pipe and a stainless steel adapter is welded to the pipe. The sensor is then twisted manually into the adapter.
The sensor''s ability to sit flush on the pipe makes it ideal for pharmaceutical applications. Its base is completely smooth and grooveless, preventing media from sticking and warding off contamination. Easy to clean, the sensor can be removed quickly from the pipe, and its design meets 3A, FDA, and EHEDG requirements.
The sensor''s visual indication was another selling point for FMC. ifm efector pressure sensors feature a 3-digit numeric display that is particularly useful for immediate pressure status, especially in low-lit areas. The ability to see the sensor''s numeric pressure reading from across a room is a great benefit in troubleshooting. The display also allows access to a microprocessor-based programming menu to input analog start- and end-points. Through one of these menu options, the face of the sensor can be rotated to read right side up, even when the sensor is facing the opposite direction on a vertical pipe.
Price was also an issue that gave ifm efector an edge over the isolator. With extreme accuracy, numeric display, simple mounting, and easy installation, ifm efector pressure sensors are less than half the cost of a typical pressure isolator.
In the past year, FMC has replaced the pressure isolators in its slurry application with ifm efector pressure sensors. During the last 12 months, ifm efector pressure sensors have proven extremely reliable. FMC''s Jerry Daniels sums it up: "It''s a low-cost solution that''s reliable, and it was a success from the beginning."