Controlling And Automating A Continuous Process Industry Plant
Automating and controlling the Tajna River Industries manufacturing unit with a custom system.
Using NI LabVIEW software to create an automation and control system that reduces inputs, manpower, power consumption, and down time
Tajna River Industries is a continuous process chemical industry that manufactures bleached lac, shellac flakes, shellac wax, and seedlac. In addition to production floors, we also have a water treatment plant, chiller units, a steam producer, a sodium hypo chlorite preparation plant, a gasifier (wood to producer gas), and diesel generator (DG) sets.
We wanted to improve our system by reducing inputs, manpower, power consumption, and down time. With a new system based on virtual instrumentation, we accomplished the following
1. Speed Control of DG Sets: The DG sets are powered by a mixture of diesel and producer gas produced in an 80 kW gasifier. The engine speed increases as more gas is input, so we must reduce the diesel fuel intake to achieve a constant engine speed and line frequency. We detect the engine speed by using LabVIEW to find the frequency of the tone generator output attached to the engine shaft. The closed-loop control system implemented in LabVIEW generates signals through the multifunction NI data acquisition (DAQ) device to control diesel flow in the engine. The output from the DAQ device is applied to a small DC motor through a DC regulator IC that screws or unscrews the fuel control screw of the generator (see Figure 1).
2. Power factor control: The system performs power factor sensing through the analog signal from a power factor transducer. The signal is fed from the multifunction I/O DAQ device to the control system built in LabVIEW. The control system has a set of digital outputs that switches on and off 24 relay switches. These relay switches control contactors that add or remove 15 capacitors in a capacitor bank so the power factor remains close to the desired 0.92 setpoint (see Figure 2).
3. Automatic Control of Chiller Machine: Previously, we used a Siemens programmable logic controller (PLC) for the chiller machine, but it had costly spare parts and problems with the PLC main card, so we decided to replace it with a LabVIEW-based system. We monitor temperature at five points in the machine. The chiller machine is energized by steam, which we control by first generating a ramp output during a 12-minute span from the DAQ device attached to a system that supplies steam to the high-temperature generator of the chiller machine. Using LabVIEW, we implemented automatic switch control to open and close the steam valve from 100 percent to 0 percent. Water is cooled to 4°C and the steam control valve is modulated depending on the current temperature (see Figure 3).
4. Electric Load management: The total connected load is 75 kVA and 85 kVA in two units. We must manage the load to avoid going beyond the maximum limit or exposing the system to instability. We use the same load management system to remove the possibility of sudden loading on the DG Sets (125 kVA, 110 kVA, 40 kVA, or 20 kVA depending on load needs) when attempting to start several loading units at the same time. We run 80 subunits through this power supply. We introduced a scheme in which each piece of equipment releases a pulse for a duration of its startup. This varies depending on the type of equipment such as fans, centrifuges, pumps, and motors. We implemented sequence starting on a first come, first serve basis using digital I/O cards. We use LabVIEW to log the starting and stopping of various units (see Figure 4).
5. Maximum Demand Control: With maximum demand control, we prevent the multiple power sources from becoming overloaded. Before starting a load, we verify the running load and load limit of the power supply. We know the load that is added to start a particular load, the running load of the source, and the load limit of a power source. Based on these simple calculations made in LabVIEW, the system accordingly gives permission to start on a particular source. If the power supply changes, then the changed load limit and running load are updated. Following a similar algorithm to account for frequency considerations for DG sets, a starter cannot start a DG set if it is running on low frequency.
6. Plant Maintenance Scheduling: Because the system keeps record of starting and stopping each unit, we can easily calculate the number of run hours for each piece of equipment. We can schedule plant maintenance based on the run hours. A maintenance alarm activates after a set number of run hours. We use online condition monitoring in other areas as well. For example, we can check the temperature and vibration of bearings and motors to determine if they need maintenance.
This system had several benefits such as Capital cost reduction, improved monitoring & control of plant & machinery, man power reduction, power system stability, savings in power tariff, better care of equipment through Plant Maintenance System. All these benefits could be achieved through just one system and one platform LabVIEW and it also made it possible to use the existing hardware which other wise would not have been used.
LabVIEW, along with high-density, low-cost hardware, is an ideal platform on which any engineer or production manager can implement their ideas to improve their system and profits. LabVIEW training taught us good programming practices, which drastically reduced development time (see Figures 5 and 6 for sample VIs). The schemes we created can apply to any continuous process industry such as paper, textile, and chemicals and offer unmatched benefits. The ideas behind our system are an accumulation of years of industrial experience, but they could only become a reality with LabVIEW. LabVIEW turned our dreams into a real system.