Pipeless plant

Pipeless plants are an alternative to the traditional recipe-driven multipurpose batch plants with fixed piping between the units. In this production concept, the batches of material are moved around between stationary processing stations in mobile vessels. The processing steps are performed at different single purpose or multipurpose stationary units but the material remains in the same vessel throughout the production process. The transportation of the mobile vessels can be realized by a transportation system that is fixed to the vessels or by automated guided vehicles (AGV) that pick up the vessels only to perform a transfer order [1]. 

In comparison to traditional recipe-driven multipurpose batch plants, pipeless plants provide a significant increase of flexibility. 

Because of the high standards for the avoidance of leakage and reliability, up to now the application of the pipeless plant concept is limited to plants with moderate processing conditions (low pressures and temperatures, in most cases atmospheric pressure) [2],... 

During the plant layout as well as during the operation of pipeless plants a large number of degrees of freedom including many discrete decision variables arise from the increased modularity and flexibility and these decisions strongly influence the profitability of the plant. 

The simulation of a production run of a pipeless plant is realized by a 2-level algorithm which incorporates a scheduling module, a routing module and a simulation module. 

In co-operation with a German chemical company, a recipe-driven batch process was modelled and simulated using PPSiM. In the simulation study, different pipeless plant scenarios were tested and evaluated. The plant under consideration produces a set of consumer care products. 

The motivation for the investigation of a pipeless plant as an alternative production concept was the increasing product diversification and the decrease of the individual production volumes. It is expected that the capacity and the flexibility of the existing standard multipurpose plant that consists of several batch mixers will be not sufficient to meet the market demands and to stay economically competitive in the future. 

The objective of the simulation study therefore was a comparison of the profitability and the flexibility between an existing standard multipurpose plant and different conceivable pipeless plant scenarios. Based on the production data of the existing plant, an optimal pipeless plant setup was developed and representative production plans were simulated and evaluated. 

The simulations evaluated different pipeless plant setups starting from a basic configuration. The scenarios differed by the numbers of stations and of AGVs. As the evaluation criterion the overall production time of the production plans was used. 

After a simulation-based design of an efficient pipeless plant had been performed, the existing standard multipurpose plant was modelled by a reference model and compared to the pipeless plant setup by determining the overall production time for different production plans. 

Comparison ofthe Plant Concepts To be able to compare the pipeless plant concept with the existing multipurpose batch plant, a reference plant was modelled using PPSiM. In the existing plant three conventional batch mixers work in a shifted parallel fashion. The three batch mixers were modelled by three stations and equipped with all technical functions necessary for the production of all recipes. Therefore each batch could be processed at one of the stations and the vessel transfers were limited to the transportation of empty or loaded vessels. All the other parameters of the model, e.g., charging mass flows, the durations of vessel cleanings and the recipes remained unchanged. 

In order to be able to compare the production times of the reference plant with the pipeless plant (in basic configuration 2), the following production plans were simulated ... 

Table 3.4 Comparison of a standard multiproduct plant and a pipeless plant...

The comparison of the two plant concepts shows that the pipeless plant concept leads to smaller production and processing times at batch sizes of200 and 500 kg. This advantage decreases towards smaller batch sizes. 

At batch sizes of 100 kg the standard multipurpose plant becomes superior to the pipeless plant with respect to the processing time. The reason for this is that the CIP times of the stations and the transfer times of the vessels remain constant in both cases and therefore the portion of the duration of the productive operations becomes smaller in comparison to the processing time. The advantage of the production of several batches in parallel is therefore reduced by the increasing portion of the cleaning times of the stations. 

Assessment of the Plant Concepts The economic comparison of the pipeless plant developed in this study with the existing multipurpose batch plant resulted only... 

The pipeless plant concept leads to 20% shorter processing times for batch sizes between 200 and 500 kg, what clearly reduces the manufacturing costs of the products. By the distribution of the technical functions on several stations, the transport of the intermediate products in mobile vessels and the cleaning of the vessels in separate cleaning stations, the utilization of the stations rises and in parallel the productivity of the plant is increased. 

Further advantages result from the immanent flexibility of the pipeless plant concept. By the possibility of storage of intermediate products during the production, urgent orders with a higher priority can be preferred or inserted into the production plan. 

For the investigation of logistic questions or for the design of pipeless plants, like in the presented use-case, PPSiM offers a suitable solution. The comparison between the two plant concepts showed that the developed pipeless plant configuration leads to 20 % shorter processing times for similar investments, due to the higher utilization of the plant equipment. 

Liefeldt, A. and Engell, S. (2003) A modeling and simulation environment for pipeless plants. Proceedings of 2003 International Symposium on Process Systems Engineering (PSE 2003), Kunming, China, pp. 955-961. 

Another important aspect of process flow requirements is reflected in inventory policies. These often involve finite and dedicated storage, although frequent cases include shared tanks as well as zero-wait, non-intermediate and unlimited storage policies. Material transfer is often assumed to be instantaneous, but in some cases such as in pipeless plants delay is significant and must be accounted for. 

The concept of the disposable batch plant was further extended by using robotic systems, moving plant items from station to station, referred to as the table-top pipeless plant As an example of the use of this concept, an ethanol production unit was outlined consisting of a fermenter/stillpot, topped by a packed column section, and a partial reflux condenser. 

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