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Cellulose (2025) 32:1835–1850
addressed in the current study. Three pulp types were evaluated, namely, bleached hardwood, mechanical or groundwood as well as recycled pulp as each repre- sents a specific category of pulping processes imple- mented in the South African Pulp and paper industry.
was contained. The valves could also be used to gen- erate much longer pulses. The desired dwell time was achieved by rotating the spindle at a specified veloc- ity using a motor. A standard Programmable Logic Controller (PLC) with a high-speed card along with a dashboard or a screen for display was utilised to monitor and control the operating speed during each test. A separate high-speed data acquisition was used to log high-speed pressure readings as it was beyond the operating parameters of the standard PLC.
Development of the laboratory suction box
Novel laboratory suction box design constraints
A dynamic setup wit h a novel configuration wa s con- structed through an analysis of previous configura- tions reported in the literature, to simulate the condi- tions that exist in suction boxes. Table 1 provides a summary of requirements that were fulfilled by the novel configuration, followed by various design fac- tors considered.
Vacuum reservation mechanism
Three vacuum reservoirs each with a capacity of 50 L were included in the setup to provide enough storage fo r the required vacuum conditions. Each reservoir was fitted with a pressure gauge to monitor the vac- uum pressure. A manifold connected the reservoirs to the vacuum chamber housing the spindle, vacuum source as well as the solenoid valve bank. The system could be evacuated to the desired vacuum pressures using an ejector, which was specifically chosen as it required less maintenance due to the lack of moving parts and easy detection of leakages (Kent 2018). Previous configurations have shown signs of exces- sive air leakage during evacuation and dewatering of pulps. This occurrence seemed prominent in the studies done by Pujara et al. (2008a, b) and Räisänen et al. (1995), as previously discussed.
Pulse-generating mechanism of novel laboratory suction box
Pulse generation was achieved by implementing a slotted spindle residing beneath the sample holder as shown in Fig. 1. The spindle is inside a vacuum cham- ber. It has five slots, each with a width and length of 38.2 and 150 mm, respectively whereby the latter was chosen to match the sample diameter. Each pulse was the result of the spindle slot aligning with the vacuum port opening or slot directly below the sample holder dur ing rot ation. A pressure transmitter was placed inside the vacuum port to capture the pressure drop s occurring during pulse generation. A solenoid valve bank regulated the distribution of vacuum from the reservoirs to the chamber within which the spindle
Control philosophy
Test conditions were controlled where pulse duration as well as the dwell time were specified, after which the motor would rotate at the appropriate speed to generate
Table 1 The design requirements and constraints of the novel laboratory suction box
Variable/Parameter
Test Range
Manipulated variables Vacuum pressure
− 10 to − 60 kPa gauge
Spindle speed
400 m/min
≤ 11 0 m 3 /min m 2
Ai r flux
Singe pulse dwell/suction time
≥ 6ms
Controlled variables Grammage oven-dry
17 0g/m 2
Incoming pulp solids content o r mass concentration Measured output Outlet solids content or pulp concentration (%)
4–7%
Vol:. (1234567890)
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