BACKGROUND OF INDUSTRY

The range of PVC compounds in plastic industries include those used in the

manufacture of wires and cables, PVC pipes, footwear, doors and window profiles and

garden hoses. The plastic industries have earned a reputation of being a dependable and

creditable manufacturer of high quality plastic compounds and this had been achieved as

plastic industries have employed an intelligent and efficient process monitoring by

interfacing knowledge-based systems and multivariate statistical monitoring.

PVC is produced by polymerizing vinyl chloride (VCM), a highly toxic and explosive

chemical intermediate which is manufactured strictly for this purpose. The process of producing

VCM from raw materials is sensitive and requires careful monitoring to avoid contaminated

products and equipment failure. Typically, VCM is made by thermal cracking of ethylene

dichloride (EDC, formally 1,2-dichloroethane), which is produced on site from feed stocks of

ethylene and chlorine. Maintaining yield purity and conversion efficiency throughout the various

stages therefore requires continuous online monitoring of the production stream composition.

THE NATURE OF THE PROBLEM

(Figure 1: A general and simplified VCM production process with measuring locations)

(Table 1: Sampling points and measuring details of a VCM production plant based on Figure 1)

The problem arises when the sampling points or stream consisting of these specified components

does not comply with the measuring range which causes several problems such as contamination

in effluents, runaway reaction and many others.

Some of the nature of problems includes the contamination of EDC (ethylene dichloride) with

FeCl3, which is the catalyst for direct chlorination process. Thus, there is a need for monitoring

FeCl3 and Cl2 in EDC (sampling point 1; refer to Figure 1) as these contaminations are highly

corrosive compounds which fouls machinery and also forming cokes which causes the VCM

product quality to deteriorate drastically.

Not only that, the moisture level in EDC distillation (streaming point 5,6,7 and 8; refer to Figure

1) that exceeds 100 ppm will form a corrosive mixture with HLC and Cl2 wherein the H2O will

aggravate the corrosive effect of the produced EDC and VCM stream. The moisture also carries

other undesirable impurities which reduce the quality of these products. VCM process operators

typically measure 0-200 ppm moisture at these analysis points for process control. Besides that,

the vent gas (waste gases such as CO, CO2 ethylene and oxygent) will tend to exceed the

flammable limit when the amount of O2 exceeds 15%.

Also, the batch production process of poly(vinyl chloride) (PVC) are often monitored using

realtime measurements. Due to the lack of instrument robustness or sample preparation time,

most plant variables are difficult or even impossible to measure on-line. Such process variable

includes the temperature, wherein the production of PVC is highly exothermic that will lead to

the liberation of unnecessary heat and thus, leading to runaway reactions. Therefore, the

monitoring of process variables are required by studying the trajectories of the process variables

over time (process monitoring).

THE MONITORING SOLUTIONS

To monitor Cl2 in direct chlorination effluent stream, the OMA-300 process analyzer is

employed in which this analyzer uses a high resolution disperse UV-Vis spectrophotometer that

provides unrivaled dynamic range in measuring chlorine compounds from trace to high

concentration. This helps to prevent contamination of coke and HCL from unwanted reactions

between FeCl3 with water which will cause a loss of VCM product quality.

Besides that, any contaminations in the streams can be monitored by the use of a gas

chromatography, where this standard equipment is used to measure impurities in trace

concentrations in streaming point 2 and 5 (refer to Figure 1) which then helps to ensure

compliance with product specification and quality. Gas chromatography is also used to monitor

ambient air for chemical compounds that may emerge from certain plant units in case of sudden

leakages during emission (Siemens AG, 2007).

Also, the OXYMAT 6, an extractive continuous gas analyzer is employed to detect and monitor

the presence of highly corrosive gas produce (HCL). This corrosion proof design allows analysis

in the presence of highly corrosive gases and due to its ultrafast response, the OXYMAT 6 is

perfect for monitoring safety-relevant plants. Not only that, the in-situ Laser Spectrometer LDS 6

can be used to monitor the HLC in the ppm range of 0-3%, wherein it is a diodie laser-based in-

situ gas analyzer for measuring specific gas components directly in a process gas stream

(Siemens AG, 2007). Measurements are carried out free of spectral interferences and in real-

time, enabling pro-active monitor of dynamic processes.

To ensure that the oxygen level does not exceed the flammability limit (>15%) and to monitor

the flow of oxygen at streaming point 1 and 3, OXYMAT 65 is used as a gas analyzer based on

ZrO2 technology to measure smallest oxygen concentrations in pure gas applications (Siemens

AG, 2007).

To monitor the moisture level in EDC and VCM, the MicroSpec MCP-200 modular IR analyzer

is employed in which it is designed for simple reliability in continuous moisture measurement.

This solid state device has a zero offset feature which removes the need to obtain totally dry

zeroing fluid, thus making the Auto Zero functionality practical and inexpensive without

sacrificing accuracy. This system provides fast response 0-200ppm moisture reading required for

tight VCM process monitor (AN-030, 2013)

Modular analyzers such as the MicroSpec series analyzer have a series of rugged, ultra-modular

concentration monitors that reads the concentration outputs from all the connected MicroSpec

units, wherein this design maximize the system uptime and at the same time minimizing the

system’s physical footprint (AN-030, 2013) This analyzer provide real-time readings within

seconds and this can be used in the VCM balanced process where there are several points of

feedback control (ethylene feedstock flow rate) which require fast response time. Therefore, by

using this modular analyzer, the vent gas emission can be monitored and thus be controlled to

prevent these gases from exceeding the flammable limit.

JUSTIFICATIONS ON HOW THE MONITORING SOLUTION FITS INTO

THE DESIRABLE CHARACTERISTICS.

4.1 Quick Detection & Diagnosis

4.2 Isolability

4.3 Robustness

4.4 Novelty identification

4.5 Classification error estimation

4.6 Adaptability

4.7 Explanation facility

4.8 Modelling requirements

4.9 Storage and computational requirements

4.10 Multiple fault identification