Читать книгу Profit Maximization Techniques for Operating Chemical Plants - Sandip K. Lahiri - Страница 74

Distillation is the largest separation unit in any refinery, petrochemicals or chemical plants. Though distillation is considered the most efficient separation process among other separation processes, a distillation column consumes a lot of energy in terms of steam in reboilers. Steam costs in various distillation columns constitute a large chunk of operation costs and in most cases are the second largest contributor to the cost component after raw material costs. Not only the operating cost but also large distillation columns and their presence in sheer large numbers in any CPI, contribute heavily to the plant's initial investment cost. In short, any CPI distillation unit contributes a very large percentage of both capital costs and operating costs. Therefore, any strategy to reduce capital and operating costs of distillation columns have a significant impact on plant profitability and the strategy can be seen as a multiplier, i.e. it can be applied to many distillation columns already present in the plants.

There are three main strategies by which more profit can be earned from an existing distillation column.

 Strategy 1: Increase the feed in the distillation column to produce more products until limited by process constraints like flooding, entrainment, etc. The main constraints in the distillation column should be hydraulically stable so that it can produce an on‐spec product consistently at a higher load.

 Strategy 2: Reduce reflux to reduce steam consumption. However, the constraint is that one must always produce a required purity of the product. For an energy intensive distillation column this is a major strategy and can be considered as a problem of process simulation.

 Strategy 3: Exploit the variations in product purity or steam flow or feed flow. If there are many variations in product flow or product purity, then the column operation has to be stabilized by improving process control. Producing an ultra‐pure product (i.e. a purer product than its market specifications) has no economic benefit in the market. Impurity of the product should be at its allowable limit. Either an efflux rate reduction or feed increase has to be performed in order to reduce extra purity of product. This will increase profit. This problem can be tackled by APC.

Since a distillation operation can severely impact plant profitability, special attention is needed to optimize a running distillation column. In this step, various computation tools and modeling techniques are applied in a distillation column to maximize an economic benefit from it.