Cement Moisture Sensor

In order to produce quality cement, moisture measurement is needed at several stages of manufacturing:

Raw material extraction from a quarry

The OMNIR is installed over the conveyor belt from the surge bin in order to read the moisture content of the lime which, at this stage, is about 5-15% moisture content. A plow installed on the belt, prior to the NIR moisture sensor mount, helps to keep the cement material at a bed depth of about 3 inches (7.6 cm) and assures a smooth surface is presented to the light source from the NIR sensor. A built-in feature of the OMNIR, called Loss of Product, assures that no moisture readings are taken should there be gaps in product flow on the conveyor belt. An Internet of Things (IoT) alarm is available to alert the operator to the loss of product and the last good reading is held until product flow is re-established.

Grinding, mixing and blending

In the first stage of processing, raw calcium carbonate at 15-24% moisture content enters a crusher dryer. The material being discharged from the crusher dryer must be below 13% moisture content, but preferably between 10 and 13%, in order to prevent a product build-up inside the crusher dryer. This would necessitate costly machine down-time and labor expense for dryer clean out. OMNIR monitors the moisture content of the material that is discharged from the crusher dryer. Should the moisture content of the discharged material increase above 13%, the feed rate into the dryer would need to be decreased or the temperature within the dryer elevated.

Pre-heater stage, prior to kiln drying, in order to improve kiln efficiency

The moisture information from the OMNIR moisture meter is used in conjunction with the total weight of the material entering the kiln and is transmitted via a 4-20mA output signal (or many other optional protocols) to the dryer controller, or fed directly into the process control system. This is in order to make any corrections to the flow rate or kiln temperature, to assure on-spec product.

Prior to the introduction of the OMNIR, it was necessary to have employees constantly observe the crusher dryer operation and to carry moisture samples back and forth between the dryer and the laboratory. Often, delays in lab results resulted in off-spec product (particularly too wet), which required considerable down-time, machine restart and lost product which must be recycled at considerable expense. In one instance of a Finna Sensors’ install, by virtue of having instantaneous on-line moisture results, 8760 hours per year were saved via the elimination of personal attention required at the dryer. In addition, the elimination of shutdowns required to clear blockage from the dryer resulted in an increase in dryer production rate of 10%.

The moisture information supplied by the OMNIR moisture meter is also used to control the feed rate into the kiln. The drying kiln’s rotating furnace is controlled to about 2,642°F (1,450°C) to assure final clinker consistency. OMNIR’s output signal may be monitored by the kiln controller or fed directly into the process control system. Cooling and final grinding of the produced clinker is the final step in the production process. Final moisture is controlled to ±1% and static lab tests demonstrate an accuracy of ±0.2%.

Therefore, reported savings in time, materials, waste, and product rework have been substantial. Years to Payout calculations indicate a typical payback of much less than one year with Return on Investment of greater than 20%.

Final Quality Control

For final quality control, Finna Sensors Model B portable cement moisture meter has been designed specifically to measure moisture content in finished concrete blocks. The meter design is based on more than 80 years’ experience in the moisture testing industry. The Model B is used in conjunction with the ASTM Method C-140 to establish calibrations for over 34 different kinds of concrete block. Calibration samples were obtained from more than 18 manufacturers throughout the United States.