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『Low Flow Fuel Meter Sizing: High-Accuracy Positive Displacement Gear Sensors for Boiler Fuel Consumption』Related information(clamp on meter|electromagnetic meter|venturi meterrotameter|orifice meter|ultrasonic flow meter|mass flow meter|coriolis mass flow meter|coriolis flow meter|magnetic flow meter|magmeter flow meter|magflow flow meter|mag meter flow meter|electromagnetic flow meter|vortex flow meter|turbine flow meter|thermal mass flow meter|thermal flow meter|rotameter flow meter)
Low Flow Fuel Meter Sizing: High-Accuracy Positive Displacement Gear Sensors for Boiler Fuel Consumption
Quick Answer: For boiler fuel oil lines with minimum flow below 20 kg/h, a positive displacement gear meter with DN15 or DN10 connections is the correct choice. Accuracy of plus minus 0.5 percent of reading is possible with 4-20 mA HART output. Silver Instruments supplies oval gear flow meters for diesel, light oil, heavy oil and biofuel blends.
Sizing Starts With Minimum Flow, Not Maximum Flow
Most engineers skip this part. They read the burner nameplate maximum firing rate and pick a meter from that number. But boiler fuel consumption changes a lot between low fire and full load. A 2 t/h steam boiler in Vietnam can burn 12 kg/h of diesel at low fire and 60 kg/h at full load. The meter must stay accurate at 12 kg/h. If you size for 60 kg/h only, the low flow signal becomes noisy or drops to zero.
So we start with minimum flow. Then we check turndown. Then we check viscosity and temperature. That order works for nearly all boiler fuel oil applications we see in Southeast Asia, the Middle East and Latin America.
Why Positive Displacement Gear Sensors Work for Boiler Fuel
A gear meter traps a fixed volume of liquid in each pocket between the gear teeth and the housing. Every full rotation releases a known volume. This principle does not depend much on flow profile or viscosity. A turbine meter or an orifice plate may lose accuracy when diesel viscosity moves from 3 cP to 20 cP. A positive displacement gear meter does not have this problem.
Silver Instruments gear meters handle diesel, light oil, heavy fuel oil and some biofuel blends. Typical viscosity range is 2 cP to 2000 cP. Standard process temperature rating is 120 °C. A high temperature version for heavy oil goes up to 150 °C. Pressure rating is 40 bar for standard threaded or flanged connections.
Parameter Checklist for Boiler Fuel Meter Sizing
Send us four process values. Minimum and maximum flow in kg/h. Operating temperature in °C. Viscosity in cP. Pipe size in DN. That is enough for a first sizing pass. For a diesel boiler line at 5 cP, a DN15 gear meter covers about 0.5 to 100 kg/h. A DN10 meter covers 0.1 to 30 kg/h. A DN20 meter covers 2 to 200 kg/h. Do not match the meter size to the existing pipe if the turndown is high. A DN15 meter with reducers on a DN25 fuel line often works better than a DN25 meter that loses accuracy at low fire.
Here is the thing. Low flow accuracy is more important than peak flow capacity in boiler service. The burner spends most of its time below 70 percent load. A meter that reads zero at low fire gives you no consumption data for energy audits or fuel billing.
Output, Display and Hazardous Area Options
Most boiler control systems need 4-20 mA HART for BMS or PLC input. Pulse output is useful for totalized fuel consumption. A local LCD display helps operators read flow during maintenance rounds. Silver Instruments supplies the OGM-DN15 with all three signals together if needed.
For heavy fuel oil with viscosity above 200 cP, add a PT100 temperature sensor to the meter body or the fuel line. The 4-20 mA HART output from the meter and the PT100 signal together give the control system enough data for viscosity correction.
For boiler rooms and fuel skids in hazardous areas, choose ATEX Zone 1 or Zon
Recommended Silver Instruments Model
The common starting point for low flow boiler fuel is the Silver Instruments OGM-DN15 positive displacement gear flow meter. Typical specifications for diesel at 5 cP are as follows.
- Flow range 0.5 to 100 kg/h
- Accuracy plus minus 0.5 percent of reading
- Repeatability plus minus 0.1 percent
- 4-20 mA HART and pulse output
- DN15 threaded or flanged process connection
- 316L stainless steel body
- ATEX Zone 1 option
- Local LCD display
For heavy fuel oil above 200 cP or process temperature above 120 °C, we recommend the high temperature version with tungsten carbide bearings and a heating jacket option.
Installation Notes for Boiler Fuel Lines
Gear meters need a 60 mesh filter upstream. Fuel always contains small particles. Without a filter, solid particles can score the gears and change the meter factor. Install an air eliminator or a gas release valve if the fuel line may contain vapor bubbles. Positive displacement meters do not need long straight pipe runs. Five pipe diameters upstream and two downstream is enough for normal boiler fuel service.
A customer in the Philippines replaced a turbine meter on a diesel boiler. The turbine meter lost signal at low fire because the fuel viscosity changed with temperature. We installed a DN15 Silver Instruments gear meter with a 60 mesh filter. The low fire reading became stable at 14 kg/h. That solved the data gap for the plant energy report.
FAQ: Low Flow Fuel Meter Sizing for Boiler Fuel
Q: What is the minimum flow a DN15 gear meter can measure for diesel?
A: For diesel at 5 cP, a DN15 positive displacement gear meter from Silver Instruments measures from about 0.5 kg/h up to 100 kg/h. Accuracy stays within plus minus 0.5 percent of reading above 2 percent of full scale.
Q: Can I use a positive displacement gear meter for heavy fuel oil HFO?
A: Yes. The wetted parts and bearing design need to match viscosity and temperature. For HFO up to 2000 cP and 120 °C, we supply a high temperature version with 316L body and tungsten carbide bearings.
Q: Do I need a straight pipe run before the gear meter?
A: No. Positive displacement meters do not require long upstream straight runs. A filter and air eliminator matter more for boiler fuel lines.
Q: Which output signal should I choose for boiler fuel consumption?
A: 4-20 mA HART is the most common for BMS and PLC integration. A pulse output is also useful for totalizer readings. Many sites use both.
Q: What details should I send to Silver Instruments for a fuel meter quote?
A: Send us fuel type, viscosity in cP, minimum and maximum flow in kg/h, pressure in bar, temperature in °C, and pipe size in DN. We will reply with a sizing table and a firm price.
Send us your fuel type, viscosity in cP, flow range in kg/h, pressure in bar, temperature in °C, and pipe size in DN. A sizing engineer will reply with a model number and price. You can reach Silver Automation Instruments at Tel: +86-25-68650347, Whatsapp: +86-25-52155837, WeChat: +86 15365082610.