Utility systems
Title: Pressure Vessels
Author: David Chen
Steward: Fengqi You
Date Presented: January 13, 2014 /Date Revised: January 14, 2014
Introduction
Many chemical processes do not take place at ambient temperature or pressures. In order to reach these non-ambient conditions, utilities will have to be used to raise or lower temperatures and compress gases. (Towler, Towler/UOP) Utilities often contribute 5 to 10% of the price of a product, and may come from public or private utility companies or on-site plants. For purchased utilities, costs depend on consumption, while for company-owned utilities, there will be both capital and operating costs. They include things such as steam for heating, electricity, cooling water, refrigeration, fuels such as natural gas, wastewater treatment, waste disposal, and landfill. Steam is often the largest utility cost. Cogeneration unit can supply electricity accompanied with different steam pressures. (Seider 2010)
Steam
Steam is used both as a process fluid (feedstock, diluent to absorb heat of reaction, heating agent, and stripping agent in absorbers and adsorbers ) and utility. As a utility, it can be used in place. It can be used to drive pumps and compressors, ejectors (for producing a vacuum), heat exchangers to heat and vaporize. Steam is usually at 50,150, and 450 psig. Generating high-pressure steam is more costly. (Seider) There are many benefits to using steam: high heat of condensation, its temperature can be controlled by controlling the pressure, good heat transfer when condensing, nontoxic, nonflammable, and it is inert with respect to many chemicals. (Towler 107)
Electricity
Electricity is used to power many different kinds of equipment. It has many advantages:it is efficient (> 90%), reliable, available in wide range of power, shaft speeds, designs, lifetime, convenience, cost, maintenance. It is generally used up to 200 hp, and sometimes over 10,000 Hp.
The use of electricity carries with it some hazards depending on the environment. Extra care must be taken when using electrically-powered equipment in areas which may have combustible fluids, vapors, or dust, and where liquids may be present.