A common scenario often leads to incorrectly sizing pumps. In this scenario, a company decides to release a new product. The results of its marketing study project sales of 50,000 tons of product per year for the first two years. After this, sales would increase to 100,000 tons per year. An annual sale of 200,000 tons per year is projected after five years.
The engineering, procurement and construction firm (EPC) is contracted to design and build a new plant and ultimately allow for the production of the product. During the discussions between the client and the EPC firm, a mood of optimism prevails. The plant is designed to meet the future estimated capacity of 200,000 tons per year. The engineering group determines that the processes used to make the product needs a series of simulation studies to optimize the design. This includes the required mass flow rates, fluid physical properties, and the pressure and temperature requirements for each of the plant’s systems.
The mechanical engineering team uses the process flow diagrams provided by the process engineering group to size the equipment needed. The team determined the following:
The example system requires a pump with a capacity of 800 gallons per minute (gpm) to achieve the plant’s design objectives (see Figure 1).
Figure 1. This single system is one of the many interrelated systems designed for the total process. (Graphics courtesy of the author)
During the preliminary design process, the long lead items are specified early to meet the project schedule. However, the location of the equipment has not been determined. As a result, margins are factored into the design to ensure that the completed pump system is capable of meeting its process requirements.
Next, the total head required must be determined. This is done by arriving at the static and dynamic head values for the process elements.