Petroleum & Natural Gas
Weighing ton cylinders of liquefied chlorine at an oil refinery located in a tropical environment
A major brand oil refinery located near the Caribbean Sea required scales for weighing ton cylinders of liquefied chlorine. The chemical is used in several specialty processes and in treating water and wastewater.
Although the regional weather is influenced by the Gulf Stream creating a pleasing tropical environment with temperatures in the 70s and 80s, humidity often reaches 90% creating a potential for moisture damage to hardware and electronics. The Caribbean area is also a focal point for many tropical storms and hurricanes. These powerful weather systems can blow sand, mud and salt through the air which can damage scales and other equipment. Additionally, some areas around the Caribbean can receive up to 200 inches of rainfall annually which, coupled with the high humidity, can cause corrosion and rust, ruining metal parts and electronics.
The refinery needed multiple scales with ton weighing capacity, and with corrosion- and abrasion-resistance not only for scale hardware, but also for sensitive load cells and electronics. Additionally, remote monitoring of the scales was necessary. The readout had to be located at a point which facilitated centralized data gathering and allowed for efficient use of the personnel monitoring the scales.
The oil refinery conducted an extensive product review which concluded with the ordering of six Scaletron Model 3001™ Ton Cylinder Scales and two Model 1099™ Chemical Process Controllers.
Built for rugged-duty, the Model 3001 scales accurately weigh cylinders in the 2000 to 12000 pound range. The scales may be used to weigh a variety of chemicals including ammonia, carbon dioxide, hydrogen chloride, liquefied chlorine, sulfur dioxide and other liquid gases. Standard base size is 42-1/2″x24-1/4″ and accuracy is to +/- 0.5% of capacity.
Standard features include a four conductor shielded cable which can be extended through a conduit to for remote location up to 200 feet from the scale base. Current output signal is 4-20 mA, 0-20 mA or + 12 mA, -8 mA, and is selectable as active or passive. There are two independently adjustable dry contacts for use in conjunction with low level alarm systems, or automatic dialer equipment as required. The printed circuit board contains a power supply section and separate zero and span controls. Weigh meter electronics are housed in a NEMA 4X fiberglass enclosure.
Scaletron manufactured the scale bases using an epoxy especially developed to provide corrosion resistance in harsh conditions such as those in marine environments. To provide maximum protection from moisture and corrosive elements, Scaletron not only used stainless steel load cells, but also hermetically sealed the cells to assure the integrity of the strain gauge component of the cell.
A conformal coating was also used to further assure unimpeded performance of precision electronics. The coating was sprayed onto the PC boards in the scales and the indicators, and on all electronics. A conformal coating prevents ionizable contaminants such as salts from reaching circuit nodes.
Instead of the standard 4-1/2 digit LCD display, refinery project managers opted for the Scaletron Model 1099 Chemical Process Controller. The Model 1099 includes two displays — a large LED display (.56″h) to show numeric result, and a 2-line, 16-character LCD display backlit for easy reading of menu and functions.
In tropical settings, uncoated electronics and circuitry would likely be damaged by the environment causing malfunctions and possibly leading to system failure. Scaletron Scales, however, feature rugged steel construction protected by a corrosion resistant finish. The special conformal coating which Scaletron applied further enhanced corrosion resistance to act as a barrier against moisture, dust, chemicals, and temperature extremes. This provided the assurance refinery engineers needed that scale electronics had received the maximum protection from weather related hazards.
The Scaletron Ton Cylinder Scale platform features a low profile design. This makes loading an unloading cylinders easier and increases safety. Furthermore, trunnions with solid UHMW polyethylene rollers on stainless steel axles promote ease of turning cylinders on the scale.
Refinery engineers wanted the indicator box remotely located some distance from the scale. Remote mounting of the indicator eliminates the need for eyes-on monitoring at each scale thereby centralizing data gathering and allowing technicians to attend to other tasks without missing important data transmissions. The Model 1099 Chemical Process Controller readily adapts for remote location and is a powerful scale monitoring system.
The controller executes procedures based on processing data from four groups of four scales, each with four individual channels. That means information from sixteen load cells per Controller is instantly integrated creating a comprehensive, centralized database for refinery engineers. The Model 1099 sends all reporting information to a printer, recorder, or scada system, and can provide permanent records of daily usage, amount used, days till empty, and the feed rate. In addition, the Model 1099 Controller provides set-point relays that can trigger an alarm or warning light to alert workers of a low condition so they do not run out of chemical and experience down time.
From the project’s inception, Scaletron responded quickly with flexible options designed to meet specific needs. This enabled refinery engineers to review and select the options best suited to the installation.