Air- and Gas-Flow Measurement for Aeration Basins

Fluid Components's precision ST98 Thermal Mass Flow Meter, when combined with the Vortab Model VIP Flow Conditioner, minimises compressed air flow energy costs in wastewater treatment plants. In wastewater treatment plants, a variety of processes are employed to eliminate organic pollutants from water. The activated sludge method requires the pumping of compressed air into aeration basins, where a diffuser system ensures the air is distributed evenly for optimum treatment.

Large amounts of compressed air are required to ensure the aeration process operates effectively, with flow meters installed in the system piping, to help monitor the air that is released into the basins. This is essential, because the air flow controls the growth of micro-organisms that treat the wastewater. Precisely controlling the air flow is necessary to reduce compressed-air energy costs, which are one of the largest expenses in the treatment process.

The ST98 Flow Meter, in combination with the VIP Flow Conditioner, fulfils this task by offering accurate performance over a wide flow range, ease of installation and low maintenance requirements. It features a thermal dispersion mass flow sensing element, with no moving parts, which provides accuracy and reliability in harsh environments. The ST98 also includes an integral two-way Hart interface that allows engineers to receive multiple process variables and to configure the meter remotely from the safety of the control room.

The ST98 Flow Meter offers high accuracy to +/-1 per cent of reading, 0.5 per cent of full scale. Repeatability is +/-0.5 per cent of reading. This insertion-style flow meter can be installed without shutting down the process by using a simple NPT fitting. The ST98 operates over a wide flow range from 0.75 to 600 SFPS (0.21 to 172 NMPS), and the turndown ratio is factory preset from 10:1 up to 100:1. It operates at pressures up to 250psig. The Vortab Insertion Panel (VIP) Flow Conditioner compensates for flow disturbances in wastewater-treatment aeration basin compressed-air piping systems.

Flow disturbances are typically caused by elbows, valves and shorter-than-optimum upstream straight-pipe runs. Adequate pipe straight-runs upstream and downstream from the meter are necessary to ensure a smooth flow profile for proper measurement. Vortab VIP Flow Conditioners remove both swirl and distorted velocity flow profiles under challenging pipe-layout conditions. The VIP blends the performance and low-pressure drop of Vortab tab-type flow conditioning technology with the low cost and ease-of-installation of an insertion-panel-type flow conditioner.

Vortab technology reduces pressure drop compared to alternative technologies such as tube bundles, screens and perforated plates, which helps minimise plant energy consumption and energy costs. Many flow-meter technologies require several diameters of straight pipe run to meet their meter's accuracy specifications, and the Model VIP Insertion Panel Flow Conditioner solves this pipe straight-run dilemma. A VIP installed at three pipe diameters downstream from the flow disturbance, with the flow meter installed at three pipe diameters downstream of the VIP, neutralises the flow disturbance and produces a symmetrical and swirl-free repeatable flow profile.

The thin, lightweight panel design of VIP is easily installed between flanges or can be welded in place. The standard Model VIP Flow Conditioner is manufactured of 316 litres stainless steel in sizes for installation in pipes from 2-40in diameters (50 to 999.9mm). Other materials and larger line sizes are available upon request. They are available in both ANSI and DIN flange-mount or weld-in-place configurations. A typical VIP weighs less than 560g per diameter, allowing it to be easily transported and installed on site without using special handling equipment.

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