Plant single stream

Holroyd, R. Ultra Large Single Stream Chemical Plants Their Advantages, Disadvantages, Chemistry and Industry, Aug 5, 1967, p. 1310. 

A single-stream plant was required (minimum installed spares/duplicated machines) but with greater than 95% uptime. 

Factors that affect the safety of a production system include (1) the scale of production (2) the quantity of hazardous chemicals involved (3) the hazardousness of the chemicals involved (4) batch versus continuous processing (5) the presence of pressure or temperature extremes (6) storage of intermediates versus closed loop processing and (7) multi-stream versus single-stream plants. These factors are discussed briefly below. 

Multi-Stream Versus Single-Stream Plants... 

Commercial plants The process is used in 19 plants with an annual production of around 3.8 million metric tons (mtons) of VCM. A single stream plant with an annual capacity of 400,000 mtons of VCM was commissioned in a record time of two months in September 2004. One VCM plant with an annual capacity of 300,000 mtons of VCM is under construction. 

The second phase started during World War II and culminated in the commercialization of the large single-stream plant in the 1960s. 

Essentially one stream of the old continuous refinery plant was demolished to make way for the installation of five 420 tonne pans, allowing batch refining to commence at reduced capacity. It was a significant achievement that single stream batch refining was successfully commissioned while operators lacked access to walk fully around three of the new pans. 

Table 6.7 Increased capacity effect on cost plus return of a single stream versus a twin-stream plant...

Rhode Island (2013) Rhode Island to Open Single Stream Recycling Plant, Plastics News, http //www.plasticsnews.com/article/20120605/news/306059970/ rhodeisland-to-open-single-stream-recycling-plant (last accessed June 2013). 

In recent years there have been major advances in ammonia synthesis technology. These changes have resulted in increased plant capacity, improved reliability, higher efficiency, and lower capital cost. These developments came about in two stages first by the introduction of the large single-stream ammonia plant, and second as a result of the search for maximum plant efficiency. 

The last 25 years has seen an increase in maximum single-stream capacity from 500 to over 2000 ton per day (although in recent years there has been renewed interest in smaller capacity plants), with a reduction in energy consumption from over 45 MJ kg ammonia to less than 32 MJ kg . 

Two trends in plant scale are apparent. The first is a continuation of present plant capacities in the range 1000-1750 tons per day. There is unlikely to be a trend to build larger plants as envisaged a few years ago. Although single-stream plants with capacities of over 2000 tons per day are feasible, such large projects are more difficult to finance, and are likely to encounter constraints of feedstock availability and product marketing. 

The end product of the development described above (and in more detail in [25]) was, as mentioned, the large capacity single stream ammonia plant. 

From 1940, when synthesis gas first was prodnced from natural gas rather than coal, single-stream ammonia plants were developed and the process was subject to an ongoing series of improvements. Improved catalysts based on the same natural magnetite were made as the internal structure of magnetite and the function of the promoters could be investigated with modem analytical procedures. Catalyst life with purer synthesis gas can now exceed 15 years. 

The urgent demand for better catalysts intensified in the late 1950s as polyethylene production was developed and new plants in Europe began to use naphtha feeds. Larger single-stream ethylene plants needed better reliabihty and selectivity from more active catalysts. In the short term, better acetylene conver-... 

The introduction of the first 1000 tons per day high-pressure steam reformers in single stream plants led to some operating difficulties. For example, the new high heat flux reformers developed overheated bands, about one third of the way down the reformer tubes. Hot bands, as they were called, resulted from the deposition of carbon from the thermal cracking reaction as the catalyst lost activity. Carbon can most easily form from methane cracking ... 

In modem, single stream ammonia plants there is little scope in the design to make significant changes to the operating conditions in any of the individual catalyst reactors. Operating conditions for the carbon monoxide conversion reaction are shown in Table 9.14. The only practical variable is operating temperature which can be slowly increased as catalyst loses activity. 

Carbon monoxide also reacted with magnetite forming carbides which catalyzed the production of hydrocarbons by Fischer-Tropsch reactions. It has since been shown that both reactions can be suppressed by the addition of copper to the existing iron-chromium catalyst. This has allowed operation of HTS catalysts in existing plants down to a steam ratio as low as 0.4 compared with about 0.6 in the early single stream plants. 

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