White Coal in Thermic Fluid Heaters: Suitability, Setup and Operating Tips

Thermic fluid heaters sit quietly behind many textile stenters, dryers, chemical reactors, food fryers and paper-line cylinders, delivering hot oil at a steady temperature without the pressure of steam. When the fuel bill climbs, engineers naturally ask whether white coal, the common name for biomass briquettes, can replace coal or wood in a solid-fuel heater. The honest answer is that it often can, but it depends on the design of your heater and on a few checks you should complete before the first bag is loaded.

How a Solid-Fuel Thermic Fluid Heater Works

A thermic fluid heater does not boil water. A circulation pump pushes thermal oil through one or more coils inside the combustion chamber, the oil picks up heat, and it then travels to your process equipment and returns cooler. The fuel side of a solid-fuel unit has four main parts.

Grate, Feeder, Air and Stack

The grate holds the burning bed of fuel. It may be a fixed grate that is hand fed or a moving or stoker grate fed by a screw or hopper mechanism. The feeder meters fuel onto the grate in response to the load. Combustion air arrives in two streams: primary air from beneath the grate and secondary air above the bed to burn off volatiles. An induced draught fan pulls flue gas through the coils and out through the stack. The whole system is balanced around the fuel it was designed for, which is why switching fuel is an engineering decision and not just a purchasing one.

When White Coal Is a Good Fit and When It Is Not

White coal tends to suit heaters that already burn solid fuel, because the grate, feeder and draught system exist and mainly need to be matched to a new fuel size and burn behaviour. It is a sensible candidate when your heater runs on coal, wood chips or other biomass today, when its load is reasonably steady, and when the maker's design allows a fuel in the calorific range of our briquettes.

It is a poorer fit in several situations. A heater designed only for oil or gas has no grate or feeder, so it is not a candidate without a major rebuild. A unit with a very small grate may struggle to carry enough fuel at peak load, because briquettes at 3800 to 4200 Kcal/kg may need more fuel by weight than a higher-grade coal. A heater with a hard-to-clean combustion chamber or weak draught can suffer from ash build-up. White coal is not a one-to-one replacement for every coal. The deciding voice should be your heater manufacturer, who knows the furnace volume, grate loading limits and coil design. Ask them in writing whether the unit can be fired with 90mm briquettes and at what rated output.

What to Check Before You Switch

The table below is a practical pre-switch checklist. Work through it with your maintenance team and, where noted, with the heater maker.

Pay particular attention to safety interlocks. A thermic fluid heater runs at high oil temperature, and the protective trips for low oil flow, high outlet temperature and loss of flame are not optional. A different fuel changes how quickly the furnace responds to a change in feed, so ask whether trip set points and the temperature control loop should be reviewed.

Fuel Characteristics That Matter

Four properties of the fuel decide how it behaves in your heater. These are BBI's own specification for our briquettes, confirmed by the batch lab report, which is available on request.

• Size: 90mm diameter briquettes, which suit most screw and hopper feeders but should be tested in yours.
• GCV: 3800 to 4200 Kcal/kg, which sets how many kilograms you need for a given heat duty.
• Moisture: below 10 percent, so less heat is spent evaporating water and ignition is easier.
• Ash: below 10 percent, typically 2 to 8 percent depending on feedstock, with sulphur below 0.1 percent.

For a deeper look at how calorific value is measured and read, see our guide to GCV in biomass fuels. Compared with typical Indian coal, which is generally 25 to 45 percent ash, lower-ash briquettes leave less residue to handle, but you should still plan ash removal for your own fuel and load.

Start-Up and Load-Following Tips

These tips are qualitative, because every heater and process behaves differently. Follow your manufacturer's start-up procedure first, and use these as supplements.

Light-Up

Start with a modest, well-spread bed rather than a heavy charge. Let the fire establish and the oil temperature rise gradually, with the circulation pump running throughout, so the coils are never heated without flow. Briquettes ignite more slowly than loose chips, so allow the bed to build before asking for full output.

Following the Load

Briquettes burn steadily and hold their shape on the grate, which many operators find helpful for a stable outlet temperature. Adjust the feed rate and the primary and secondary air together, in small steps, and watch the fluid outlet temperature rather than chasing it. Large, abrupt changes in feed are the usual cause of temperature swings with any solid fuel. If your process load changes sharply, discuss with the heater maker whether the feeder control can be tuned for smoother response.

Keeping the Fuel Dry and Intact

Store briquettes under cover and off the floor. Wet or broken fuel burns unevenly and creates fines that can choke feeders. Our storage and handling guide covers the basics.

Maintenance Points to Watch

We do not give fixed cleaning intervals, because they depend on your heater, your load hours and your fuel batch. Instead, set your own intervals during the trial by observing the plant and recording what you find.

• Soot and deposits on the coils reduce heat transfer, so watch the flue gas exit temperature and the heat-up time as early signs.
• Ash removal from the grate and ash pit should be kept regular so that air passages stay open.
• Draught fans and feeder screws wear with use, so listen for changes in noise and watch motor load.
• Inspect refractory, grate bars and doors for damage after the first weeks of operation on the new fuel.
• Keep thermic fluid quality checks and interlock tests on your normal schedule.

A 25 MT Trial Plan

Our minimum order quantity is 25 MT, which makes a practical trial batch. Here is a sensible structure.

1. Share your heater make, rated duty, grate details and current fuel with us, and get the heater maker's written view on briquette firing.
2. Ask for the batch lab report and check GCV, moisture, ash and sulphur against the specification above.
3. Record a baseline on your current fuel: fuel used per shift, outlet temperature behaviour, ash quantity and flue gas temperature.
4. Run the 25 MT on normal production, with your operators and the heater supplier watching feed, air and temperature.
5. Record the same readings, note jams, fines, soot and ash, and compare with the baseline before deciding on a longer contract.

For wider planning, our coal to biomass retrofit guide explains the conversion steps for boilers, and many points apply to thermic heaters as well.

Comparing Cost per Million Kcal

Compare fuels on delivered heat, not on the rate per kilogram. First, take the GCV from a lab report. Second, divide 1,000,000 by the GCV to find the kilograms of fuel needed per million Kcal of heat input. Third, adjust for the efficiency of your heater, measured on your own plant, since a heater converts only part of the fuel heat into oil heat. Fourth, multiply by your delivered price per kilogram. Do this for your current fuel and for white coal using the same method, and add the cost of ash handling and labour to each. Our guide on calculating boiler efficiency explains the efficiency step, and our fuel cost calculator lets you test the numbers with your own inputs. Product details are on the biomass briquettes page.

Textile processors may also find our note on dyeing and printing units useful, since many of them run thermic heaters for stenters and dryers.

If you run a solid-fuel thermic fluid heater and want to plan a 25 MT trial, contact our team with your heater details, current fuel and monthly requirement.