JX-300XDCS system mainly consists of one engineer station, two operation stations, two control stations, and through four HUBs to establish a double redundant industrial Ethernet. The engineer station and operation station use DELL mainframe with 2.66GHz main frequency, 256MB memory, 40GB hard disk, and equipped with 1 wide-line printer and 1 inkjet printer. The control station consists of 2 mutually redundant master control cards, 12 redundant data forwarding cards, 6 power supplies, 10 power indicator cards, 95 I/O modules and 6 cage standard kits.

Dosing Functions

(1) Engineer Station

JX-300X engineer station is mainly used for dosage maintenance, dosage setting and expansion. In continuous polyester production unit, it mainly completes program development, dosage diagnosis, controller configuration and bit number definition, development of function block diagram of control strategy, sequence control block diagram, configuration, compilation and download of dosage software, and monitoring of dosage system operation.

(2) Operation station

JX-300X operation station mainly completes the monitoring of continuous polyester plant batching operation. The real-time monitoring of automatic batching system is divided into alarm list, batching overview, control group, adjustment screen, trend chart, flow chart, data list, etc. The monitoring of the site is realized through the friendly man-machine interface.

(3) Control station

In the continuous polyester plant, the DCS system control station is mainly used for process control, logic control and data acquisition.

① Data acquisition station realizes the basic monitoring function of analog and switching signals. A data acquisition station can handle up to 384 points of analog signals (AI/AO) or 1024 points of switching signals (DI/DO), and complete the acquisition of analog and switching signals required by all feeding systems through AI and DI modules. It meets the demand of control points in continuous polyester production line.

②Logic control station adopts motor control and relay type discrete logic function; characterized by fast signal processing and control response, the control cycle can be as small as 50ms; the logic control station focuses on completing the interlocking logic function, and the loop control function is restricted accordingly; the maximum load of the logic control station: 64 analog inputs, 1024 switching quantities; complete the dosage system through the graphic programming software Sequence control, interlocking/unlocking control and calculation of output and accumulated quantity are completed by graphic programming software.

③Process control station is referred to as batching control system, which is the control station of centralized feeding system in the traditional sense, and adopts JX-300XDCS to provide all the functions of conventional loop control and sequential control scheme, and the control cycle can be as small as 0.1s; Maximum load of the process control station: 128 control circuits (AO), 256 analog inputs (AI), and 1024 switching quantities; it provides various PIDs of temperature, pressure, flow rate, and other control functions. PID single-loop and cascade loop control of temperature, pressure and flow, including vacuum and viscosity cascade control.

Detection and control of main process parameters

(1) Detection of process parameters

This dosage realizes real-time detection of various temperature, pressure, flow and liquid level parameters and feedback signal detection of on-site motor through cable. And according to the process requirements, the analog quantity point sets the upper and lower limit alarm, the switching quantity point fault signal alarm, and through the sound screen alarm of the operation station, real-time to remind the operator to carry out the necessary processing.

(2) Interlock control

Automatic feeding system in order to make production stable and protect the equipment, in the continuous polyester production line generally use a lot of interlock control. In this dosage, through the customized control scheme of the graphical programming software of the LD paragraph to achieve this function, so that the site pumps and valves in specific conditions start / stop and alarm. To enable better use of the interlock function, a start/stop interlock button has also been provided to enable the unit to be unlocked for industrial control even under abnormal conditions. This interlock is used to stop the addition of coarse EG to the kettle by triggering A21 when the kettle pressure is too high (PAHH-04310A). A21_INTER and ALM_A21 are customized one-byte variables used for start/stop interlocking and alarming, respectively.

(3) Calculation module

During the production process, it is also necessary to know the yield, the cumulative quantity and the additions to some of the main parameters. For this purpose, it is defined in the FBD paragraph of the graphic programming software of the customized control scheme. The final polycondensation section level in this unit is adjusted by controlling the pre-polymerization pump speed SC-05240 to regulate the feed volume through controller LIC-05312, where LI-05312 is calculated from the front and rear reactor levels (LT-05310 and LT-05311) by the calculation formula shown.

(4) Sequence control

In production, the slurry preparation dosing is controlled by a program. Firstly, a quantitative amount of EG is added to one of the slurry preparation reaction tanks (EG is measured by a mass flow meter), the stirrer of the slurry preparation reaction tanks is activated, and the corresponding purified terephthalic acid (PTA) is added according to the set molar ratio, meanwhile the prepared catalyst solution (CPC) is added proportionally, and waits for a certain period of time after stirring. This function can be realized through the SFC paragraph of the graphic programming software.

(5) Dosage Adjustment

The weighing and batching system uses a large number of single-loop PID control, the control parameters include: proportionality P, integral time I, differential time D, control period Ts. In addition to this, a series loop is also used. That is, when the output of one controller is required to change a given value of another controller, the two controllers thus connected are said to be in series. Both controllers have their own measurement inputs, but only the primary controller has its own independent given value, and the output signal of the secondary controller is sent to the process being controlled. The main serial loops in this batching system are ester - liquid level through the mass flow meter to control the speed of the slurry pump, the reactor's internal temperature regulation and viscosity and vacuum serial control. Some of these circuits have great hysteresis, so on the basis of the conventional cascade circuit, and through some language to realize the cascade control.

4 Comparison with imported DCS batching system

(1) Batching control

The dosage adopts Foxboro's UNIX centralized system, which is not conducive to connecting with the local area network (LAN) of the plant, especially the Internet network, and it is difficult to realize data sharing; the domestic control system adopts JX-300X to control the dosage system, and it is easy to connect with the LAN of the plant and the Internet network and share the data because of its Windows2000 operating system.

(2) Operation interface

The imported system is pure English interface, which requires higher level of Tibetan for the operator and makes the operation more difficult; the domestic control system is pure Chinese interface, which requires only short-term training for the operator to master the operation of the interface.

(3) Operability

Imported system control screen operation steps are more cumbersome, in the point of the required control screen, and then point in the box below the input data; and the domestic control in the flow chart can be opened at the same time 5 control screen, and can be directly above the input of the required data, easy to operate.

(4) Loop control

The PID loop control of the imported system is stable. Domestic batching PID loop in the regular circuit is also very stable, but in some of the more complex circuits, not as good as the imported control system, which needs to be further explored and improved in the process of using the domestic batching system.