(GP/GT) for Additional Water Supply in the Lower Rio Grande

ill-I5
The tube plates are usually rectangular and made of non-ferrous material compatible with the tubes.
Intermediate tube support plates are spaced across the vessel to maintain tube separation and prevent
vibration. In spite of continuing research into use of enhanced-profile tubes, plain circular tubes are still
the usual supply. In the cross-tube MSF plant, there may be several seawater passes through each stage,
with corresponding complexity of the waterbox designs at each end of the tube bundle. Depending on
temperature regime and fluid chemistry, water boxes are usually lined with either epoxy resin, neoprene,
butyl rubber or cupro-nickel and may incorporate sacrificial anodes to minimize corrosion/erosion of tube
ends and tube plates.
Inside each evaporator stage there are mist-separator pads, usually filling the whole horizontal crosssection
adjacent to the distillate trays. These are normally of knitted stainless steel or monel wire,
supported on a stainless steel framework. The area of the vessel shell above the mist-separator pad is
generally less prone to corrosion than the main body of the flash chamber, since it does not get splashed
with brine. It is therefore customary not to apply any protective cladding or lining to the vessel above
mist-separator level, except in the hottest one or two stages, where carbon dioxide may be released from
the brine. These hottest stages are often lined throughout with stainless steel and separately vented to the
ejector system.
At the bottom of each stage, brine boxes incorporating gates and weirs control the interstage flow and
prevent "unsealing" between stages during start-up and load changing, when liquid levels tend to fluctuate
widely. Because of the high brine velocities and extreme turbulence, these components are almost
invariably made of stainless steel.
The brine heater is usually a separate vessel in the form of conventional steam/water shell-and-tube
cylindrical heat exchanger, with carbon steel shell and non-ferrous tubes. It may have several passes on
the brine side and a number of steam entries at the top.
The venting system often incorporates a separate hogging ejector for quick start-up and either a two or
three stage ejector system, with intermediate and final condensers for normal operation. Sophisticated
materials and/or linings are often used to minimize corrosion of the ejector system under the aggressive
working conditions.
To economize on installation area, cross-tube evaporator vessels are sometimes built in a two-tier
arrangement. When considering plot layouts for both long and cross-tube MSF plants, allowance has to
be made for tube-withdrawal space. Nearly all MSF plants are installed outdoors. In places with tropical
or aggressive climates, some components such as pumps and control devices may have weather-protective
canopies or sunshades. Very small plants can sometimes be shipped and delivered to site as fully-finished
units and even for very large plants, special transport and handling facilities are often constructed as part
of the project, such that finished modules weighing up to about 2,000 tons can be brought to site and
placed on their foundations.
5. Cogeneration of Electricity and Water
By far the largest use of MSF plant is in combined-cycle (or dual-purpose) municipal installations
producing both drinking water and electricity. By combining power and water in a single undertaking,
a number of capital and operation cost savings can be achieved.