Rich/lean amine exchangers are usually shell-and-tube exchangers with the corrosive rich amine flowing through the tubes. The purpose of these exchangers is to reduce the reboiler duty by recovering some of the sensible heat from the lean amine.
The flow rates and inlet temperatures are typically known. Therefore, the outlet temperatures and duty can be determined by assuming an approach temperature for one outlet. The closer the approach temperature selected, the greater the duty and heat recovered, but the larger and more costly the exchanger. For design, an approach temperature of about 30°F provides an economic design balancing the cost of the rich/lean exchanger and the reboiler. The reboiler duties recommended above assume a 30°F approach.