LDPE plant

The autoclave is not the only component of an LDPE plant which may be exposed to a decomposition. Local hot spots in a secondary compressor may initiate a decomposition reaction consequendy it is necessary to protect these units from serious overpressure by pressure relieving devices and to release the products of the decomposition reactions safely. The problem of the aerial decomposition referred to eadier has been largely overcome by rapidly quenching the decomposition products as they enter the vent stack. 

Hypercompressors. In an LDPE plant a primary compressor, usually of two stages, is used to raise the pressure of ethylene to about 25—30 MPa and a secondary compressor, often referred to as a hypetcomptessot, is used to increase it to 150—315 MPa (22,000—45,700 psi). The thermodynamic properties of ethylene ate such that the secondary compressor requires only two stages and this results in a large pressure difference between the second stage suction and discharge pressures. 

It was concluded in 1975 that centrifugal secondary compressors with a dehvery pressure of 200—250 MPa (29,000—36,000 psi) would be feasible for ethylene capacities of more than 100,000 kg/h. However, in order to replace the primary compressor with a centrifugal machine, it would be necessary to increase the throughput to 200,000-250,000 kg/h (176). Rotary machines have yet to be used in LDPE plants. 

By using the simulation model developed in Samsung Total we applied the ideas of pFoductivily enhancement successfiiUy to LDPE plant and accomplished considerable productivity incn e. The MWD as well as the melt index and density calculated by the simulation model convinced us of applying the ideas to commercial plant. The end user property prediction capabilities of the model will be refined further by integration of phj icxjchemical and statistical approaches and be one of the next potential research items. 

The in-line safety valve [45] as shown in Fig. 4.2-7 is used in LDPE plants during emergency situations in order to depressurize the system by the outlet (2). The valve is directly included in the tubular reactor train (1) in a manner to avoid dead spaces where harmful decomposition of the polymer could take place. The control of the safety valve is effected again by a special... 

Experience from decomposition in industrial LDPE-plants as well as from laboratory experiments shows high maximum pressures and temperatures, together with extremely high rates of pressure-rise during decomposition. As can be seen from Fig. 7.2-7, top, the maximum pressure in closed bins increases steeply with increasing density of the mixture from which a decomposition starts. The maximum pressure is higher when the decomposition starts from a higher pressure and lower temperature. 

Decomposition in LDPE plants, Brochure Maack Business Services, Au/Zurich 1999. 

Economic data for a LDPE plant equipped with a tubular reactor are given as an example. The industrial unit is described in detail in Chapter 5.1. In order to show the influence of plant capacity the capital and production costs of two units for the production of 100,000 and... 

Commercial plants Many Lupotech T plants have been installed after the first plant in 1955, with a total licensed capacity of 4.4 million tons. Basell operates LDPE plants in Europe with a total capacity of close to 1 million tpy. The newest state-of-the-art Lupotech TS unit at Basell s site in Aubette, France, was commissioned in 2000 with a capacity of 320 thousand tons, it is the largest single-line LDPE plant. 

Linear low-density polyethylene (LLDPE) is used for substantially the same applications as LDPE. As the markets for LDPE have expanded, LLDPE plants have been built to supplement the supply of resin to these markets. Very few, if any, new LDPE plants have been built in recent years in fact, there are indications that LLDPE plants are being built to replace some aging LDPE units. Fortunately this is usually long after the original capital cost of the LDPE plant has been recovered from marketed product. 

For process optimization with respect to several economic criteria such as net present worth, payback period and operating cost, the classical Williams and Otto (WO) process and an industrial low-density polyethylene (LDPE) plant are considered. Results show that either single optimal solution or Pareto-optimal solutions are possible for process design problems depending on the objectives and model equations. Subsequently, industrial ecosystems are studied for optimization with respect to both economic and environmental objectives. Economic objective is important as companies are inherently profit-driven, and there is often a tradeoff between profit and environmental impact. Pareto-optimal fronts were successfully obtained for the 6-plant industrial ecosystem optimized for multiple objectives by NSGA-ll-aJG. The study and results reported in this chapter show the need and potential for optimization of processes for multiple economic and environmental objectives. 

The above background provides the motivation for the study and applications described in this chapter. Here, two types of process optimization problems are described. The first type has only economic objectives the two examples considered for this are the classical Williams and Otto (WO) process used recently by Pintaric and Kravanja (2006), and an industrial low-density polyethylene (LDPE) plant based on our recent studies (Agrawal et al., 2006 and 2007). The economic objectives tried are PBP, NPW, IRR, profit before taxes, and/or operating cost. The second type has both economic and environmental indices for this, the industrial ecosystem with four plants employed by Singh and Lou (2006) is expanded to an ecosystem with six plants and then optimized for multiple objectives. 

LDPE Plant Optimization for Multiple Economic Objectives... 

Table 10.4 gives the brief details of the MOO problems studied for the LDPE plant. Objectives in Cases A and B are the same as those used in the MOO of the WO process. Optimization of the LDPE plant for these objectives gave single optimal solution for both cases (Table 10.5). The objectives have almost the same value in both Cases A and B with only...

Table 10.4 Objectives, constraints and decision variables in the MOO - LDPE plant...

Table 10.5 Optimization of Cases A and B for the LDPE plant using NSGA-II-aJG.

Fig. 10.6 Optimization of LDPE plant by NSGA-II-aJG - Case C for clarity, results in (a) are re-plotted in (b) with suitable vertical shifts in the ordinate Cop is shown on the x-axis in all plots.

In this chapter, MOO of three process design problems is described. The first two applications - classical WO process and LDPE plant are optimized for two economic objectives such as NPW, PBT, PBP and/or Cop. For maximizing NPW and PBT, and maximizing NPW and minimizing PBP, Pareto-optimal solutions are obtained in the case of the WO process while single optimum is obtained in the case of the LDPE plant. The reason for this is the difference in the cost expressions. Pareto-optimal solutions are obtained when the LDPE plant is optimized for PBT and Cop. Hence, Pareto-optimal solutions are possible for economic objectives alone depending on the problem, objectives and cost equations. 

El Paso shut down an LDPE plant, propylene plant to Amoco. 

Comparison of the total estimated consumption with production capacities indicates that the polyolefin plants have been operating at slightly over 80% of capacity. This represents some improvement over previous years, and further improvement may result from the conversion or closing of additional LDPE plants. 

The State of Qatar was the first GCC state to have a polyolefin industry. The first production of polyolefin in the GCC was an LDPE plant inaugurated by QAPCO in 1981. In Fig. 2.8, we attempt to show in one image the historical development and ownership of this polyethylene industry. The strong French partnership is evident. The outcome, after 35 years, is the emergence of a major plant for each major kind of polyethylene. 

World-scale plants today for PE and PP are very much bigger than when the industry started, of course, by more than three orders of magnitude. Recall that the earliest ICI LDPE plants were 100 tons per annum The first 1957 polypropylene... 

Table 3.9 Emission and consumption data of LDPE plants...

Sharmina R, Sundararaja U, Shah S, Griend LV, Sun YJ. Inferential sensors for estimation of polymer quality parameters industrial application of a PLS-based soft sensor for a LDPE plant. Chem Eng Sci 2006 61 6372-6384. 

This picture did change when it became dear about two decades later that the negative market expectations for LDPE did not materialize. The favorable LDPE resin properties for film applications could not be matched by LLDPE. As a consequence, a new wave of investments in LDPE plant capacity has been initiated by the petrochemical industry. 

Figure 4.9 Training simulator image for an LDPE plant.

The concerned industries are chemical/petrochemical, power, nuclear, and armament industries, as well as high-pressure food processing. Autofrettage is common practice for equipment used in polyethylene (LDPE) plants, gun barrels, waterjet cutting pumps, and high-pressure pasteurization equipment. 

---