On-Line Microwave Moisture Analyzer for Coal Conveyors

What is the On-Line Microwave Moisture Analyzer for Coal Conveyors?

An on-line microwave moisture analyzer mounts over a conveyor and measures the dielectric response of the coal bed continuously, without touching or drying the material. It supplies real-time moisture data for boiler and blending control.

Overview

A transmitter and receiver pair, or a combined probe head, is mounted over the belt. Microwave energy passing through or reflecting from the coal bed is attenuated and phase-shifted according to its water content and mass per unit area, and a separate belt-load or thickness signal allows moisture to be separated from loading effects. The output updates every second or two and can feed boiler, mill or blending control loops. Because the instrument measures the whole stream, it avoids sampling error and reflects changes immediately. Accuracy depends on calibration against oven results using samples taken across the full belt width, and on stable size distribution and bed depth; large lumps, segregated flow, high salinity water or significant rank changes shift the response and require recalibration.

How does it work?

Water in coal is reported in more than one form. Total moisture includes free surface water and the moisture held inside the coal particles; it is measured by the reference oven method, in which a sample is dried in air at 105 to 110 °C until constant mass and the mass loss is expressed on the as-received mass. The moisture in the general analysis sample is determined the same way on air-dried, pulverized coal, and for some low-rank coals drying in nitrogen is preferred to avoid oxidation. Halogen and infrared instruments place the sample on a built-in balance and dry it with a lamp, recording mass loss continuously, which shortens the test to minutes. Microwave instruments heat the water selectively and also use mass loss. On a conveyor, microwave or neutron gauges measure moisture continuously and non-destructively by relating the response of water molecules to the mass of coal present.

What are the key features?

• Non-contact measurement above a moving conveyor
• Continuous output updated every one to two seconds
• Belt-load and thickness compensation input
• Climatic housing with window purging
• Analogue and digital interfaces for control systems
• Calibration against oven results on stream samples

What are the technical specifications?

A typical on-line microwave moisture analyzer for coal conveyors configuration offers moisture range of 0–40 %, accuracy of ± 0.5 % absolute typical, update interval of 1–2 s, belt width of 800–2000 mm, coal size of 0–50 mm typical and measurement height of 200–500 mm above bed. Values are indicative of the product class; the exact figures for each configuration are confirmed on the quotation and the calibration documents supplied with the instrument.

Which applications is it used for?

The On-Line Microwave Moisture Analyzer for Coal Conveyors is used in boiler and mill moisture control at power stations, blending and stockpile moisture management, preparation plant product moisture monitoring and coke plant coal stream logging. Across the wider Moisture Analyzers class, laboratories also deploy it for total moisture for coal shipment pricing, power station combustion and mill control and preparation plant moisture reduction control.

Which standards and certifications apply?

Relevant standards and methods include ASTM D3302, ASTM D3173, ASTM D2961, ISO 5068-2, ISO 11722, ASTM D7582, GB/T 211 and IEC 61010-1. Certification candidates for this model are CE and ISO 9001 manufacturing; each is to be confirmed for the specific configuration before shipment, and certificates are supplied only where they have been issued.

For oven methods, verify the drying temperature across the working space, keep the oven clear of wet samples during a run and cool crucibles in a desiccator before weighing, since warm or damp samples drift upward in mass. Weigh immediately after cooling and keep records of drying time, because incomplete drying biases moisture low and shifts every subsequently reported basis. Nitrogen drying requires oxygen-free gas at a controlled flow and a leak-tight oven. For halogen or microwave instruments, verify agreement with the oven at least monthly using coal samples of similar rank, and re-check after lamp or sensor replacement. On-line gauges need calibration against oven results on stream samples taken across the full belt width, plus routine checks of the electronics and, for neutron units, a formal radiation program.

How do I select the right On-Line Microwave Moisture Analyzer for Coal Conveyors?

Select the on-line microwave analyzer where continuous moisture data can be used in control, for example to trim boiler operation or blending. Specify belt dimensions, size range, installation height, accuracy target, compensation inputs and the control interface required.

How does it compare with other Moisture Analyzers variants?

Selection depends on the form of moisture you must report and the speed you need. The forced-air oven remains the reference method for total moisture and is required for contract analysis and for calibrating faster instruments, so most laboratories keep one. Halogen drying balances are convenient for moisture in the general analysis sample because they are fast, need small samples and give a printed result, but they dry only a few grams and their agreement with the oven must be demonstrated. Microwave analyzers offer rapid batch results for preparation plant control. On-line microwave and neutron gauges provide continuous moisture data for boiler control, blending and stockpile management, and need a stable belt load and a size range within their specification. Check sample mass and particle size, temperature control, agreement with the reference method, dry-gas supply for nitrogen drying, and whether results are required on as-received, air-dried or dry basis.