A sugar mill’s production team was tasked with transferring excess steam from its production system to a nearby bio-ethanol plant operated by the same parent company.
The left-over pulverised sugar cane material is burned to fuel the mill’s process steam boilers, which send steam to large turbines that create co-generation electric power.
The co-gen electric power is then used in the plant and/or exported to the power grid for use by others. Surplus plant material also can be incorporated in feed for livestock and paper product production as well.
The process engineers at the sugar mill needed a new flow meter for steam custody transfer purposes. They were required to measure the steam transferred via a 40.6 cm (16-inch) line from the sugar mill to its sister company bio-ethanol plant for cost accounting purposes.
The mill’s process engineers were looking for a reliable and accurate steam flow measurement solution without routine maintenance requirements for operation in a high-heat, high-humidity dirty plant environment.
Choosing a new flow meter can be a complex and time-consuming process. There are numerous flow meter measurement technologies, and not all of them are equally suitable for measuring all fluids: steam, gas or liquids.
A review of the plant’s process requirements, however, will generally narrow the field of candidates if the following criteria are reviewed:
o Fluid to be measured: steam at the sugar mill
o Accuracy requirement: custody transfer for plant-to-plant co-generation
o Reliability or repeatability: potentially hazardous environment
o Environment: high pressure, high temperature, high humidity
o Installation ease: straight-run requirements for accurate measurement
o Maintenance: no cleaning or recalibration
o Long Life: 25+ years
o Price: low life-cycle cost
In this particular application, the sugar mill’s high pressure operating environment was a cause for concern with some flow sensing technologies.
Those technologies that rely on moving turbines or plates can be problematic in high pressure (steam) applications. They can even pose a serious safety hazard if a piece should break off during operation and pass through the line into other equipment.
Variable line pressures occur when the steam flow is irregular due to seasonal high/low climate temperatures or changes in steam production relating to a drop or increase in feedstock. The result can be depressurisation or a pressure spike that causes stress to the mechanical parts.
After the process engineers at the sugar mill reviewed a number of flow sensor technologies, they contacted the flow measurement applications team at McCrometer.
The team at McCrometer recognised the harsh operating environment and low maintenance requirements, which led them to suggest the V-Cone Flow Meter for this application.
The V-Cone Flow Meter developed by McCrometer is suitable for use in a wide range of industries from food/beverage, pharmaceutical, pulp/paper, oil/gas, water and wastewater treatment.
McCrometer’s V-Cone Flow Meter is based on differential pressure technology requiring no moving parts that may fail due to high pressure and has no spaces that may clog during use.
Built-in flow conditioning allows the V-Cone to achieve accuracy of ±0.5% and repeatability of ±0.1% (high reliability) with straight pipe runs of only 0-3 pipe diameters upstream and 0-1 pipe diameters downstream.
The V-Cone flow meter utilises a centrally located intrusion that redirects the flow to the outside of the pipe and conditions the flow by reshaping the velocity profile, all but eliminating the need for straight pipe runs. The V-Cone flow meter requires straight pipe runs of only 0 to 3 pipe diameters upstream and 0 to 1 pipe diameters downstream.
The V-Cone flow meter’s smaller footprint requires up to 70 percent less straight pipe without being affected by flow disturbing equipment up or down stream.
Its self-conditioning design allows the sugar mill process team to place the flow meter exactly where it’s needed without the costly addition of extra pipe, external flow conditioners or complicated space-consuming layouts.
The V-Cone flow meter measures fluid flow by utilising the conservation of energy theory, which basically states that in a closed system, energy can be neither gained nor lost.
According to the PV=nRT equation, pressure multiplied by volume equals temperature while “n” and “R” are constants. Imposing a volume change within the pipe line, therefore, results in a differential pressure drop that can be measured directly.
McCrometer’s V-Cone flow meter places a “V-shaped” conical intrusion centrally in the line, redirecting the fluid to the outside of the pipe and around the cone.
One pressure sensing tap located upstream from the Cone measures static pressure while another pressure sensing tap measures the low pressure created by the cone on the downstream face of the cone itself.
The low permanent head-loss achieved by the V-Cone flow meter results from the shape of the cone itself. The shape of the cone minimises energy losses commonly caused by areas of low flow, cavitation and erratic flows.
Each V-Cone flow meter is sized to meet desired application requirements and may be specifically designed to have high or low head loss. Regardless, the overall energy consumed by the V-Cone flow meter is minimised because of its inherent characteristics.
Each meter is calibrated during the manufacturing process and because there is never a need for regular maintenance or re-calibration after installation.
The first V-Cone was installed in a sixteen-inch line and has been operating successfully since 2005. The owners of the sugar mill plant are expanding the distillery plant where they will have the same application for a larger thirty-inch (762 mm) line.
[Nick Voss is V-Cone Product Manager, McCrometer.]