case studies

If we had to choose between measuring brightness and ink count, wed choose the latter, says Rmy Simard, a process engineer at the Daishowa Inc. deinking plant. Were operating a deinking plant, and our job is removing ink.

The Daishowa mill in Quebec City, Quebec, Canada produces newsprint
and directory grades from unbleached TMP and deinked secondary fibers.

Of course brightness is an important measurement in our plant, but since we
began using brightness transmitters for continuous measurement of ink count, we have granted this parameter greater priority. And this has paid off too, says
Guy Harvey, the Technical Supervisor at the plant.

Control over suppliers
By using brightness transmitters to measure ink count, we get on-line measurements of two important parameters for the price of one. But this isnt the only benefit weve realized, continues Guy Harvey.

By monitoring the ink count we have now an excellent tool for checking the quality of incoming secondary fibers. For various reasons, what we get from them is not always what we have specified in our orders, and with ink counts we now have tangible evidence of what they have delivered. This makes dealing with them more objective.

Three sampling points
Daishowa uses three BTG brightness transmitters at three measuring points in the deinking process for monitoring brightness and ink count.

The first measuring point is positioned after coarse screening and before the flotation cell. The second is placed after flotation and fine screening but before the thickening stage. These sampling points reveal variation in brightness and ink count. The third sampling point at the end of the process and before the paper machines provides a final check on brightness and ink count so the paper machine personnel know what is coming in the line. Before installing these sampling points, variation in brightness and ink count was determined by correlating information from the brightness transmitter at the end of process with manual samples taken every two to four hours before and after flotation.
See Figure 1.

This information was too late to make a difference. After installation of the on-line sampling points before and after flotation, we gained much greater control over the process. Now we have the ability to monitor the variations, and this has improved the quality of the stock we produce, increased our productivity and lowered our operating costs, says Rmy Simard.

Ink count and brightness independent of each other
After we started continuous measurement of ink count and brightness, we found that after achieving a certain level of brightness, ink count could still vary greatly, and this was an important revelation. Brightness levels and ink count in the flotation cell are independent of each other within a certain range.

Figure 2 shows that at about the same brightness levels, the ink count can vary by as much as 100 ppm.

According to Rmy Simard this can be attributed to essentially three factors: The quality of the wastepaper raw material, the efficiency of the bleaching agent and soap and the efficiency of the flotation cell.

The total of all the information we get from the brightness transmitters helps us toward our goal of fully optimizing the process.

For instance, ink count information allows us to optimize the amounts of soap we add to the stock for ink removal in the pulper. Soap is expensive, says Rmy Simard.

Figure 3 shows the relationship between ink count on the paper machine and total hydrosulfite consumption. During the period when brightness levels were stable, the residual ink count increased from 100 to 150 ppm and the hydrosulfite dosage from 40 to 100 liters per minute.

By monitoring ink count as well as the brightness levels, we have gained greater control over the flotation cell and hydrosulfite dosages. If the ink count in the flotation cell is not within an acceptable range, we can increase the amount of TMP in the stock going to the paper machine as well as the hydrosulfite dosage to achieve a higher level of brightness, says Rmy
Simard.

Working in partnership
The development of this system for measuring brightness and ink count is a tribute to the ingenuity of the staff at the deinking plant, and it is based on their realization that brightness and ink count in the flotation cell are independent of each other.

We reasoned this way. If the wave lengths used to measure brightness in the brightness transmitter were similar to those used to measure brightness and ink count in the laboratory equipment, in principle, we could use the transmitter to measure ink count, says Rmy Simard.

Daishowa staff played around with this thought and then got in touch with
representatives from BTG. Together they worked in partnership to determine a
correlation between the various wave lengths and brightness and ink count. This collaboration has borne fruit.

Two operators and an assistant per shift operate the plant. Although the assistant still takes samples since the two sampling points were added, they are not taken as frequently. Essentially they are taken to check the transmitter probes, which operators claim are very stable. In the past six months they havent needed any adjustment at all, they say.

Figure 1.
This figure shows the excellent correlation between on-line and manual sampling of ink count.

Figure 2.
Whereas the relationship between ink count and brightness are often thought of as linear, this figure shows the two parameters to be independent of each other.

Figure 3.
Monitoring ink count and brightness levels has given Daishowa a lot of control over the flotation cell and hydrosulfite dosages.