Gas-to-gas heat exchanger for heat utilization in hot CO2 from an electrically heated calcination process

Abstract

Thesis was done with the objective of evaluating a gas to gas heat exchanger which will be used to recover heat from hot calciner exit gas from an electrically heated calcination process. Shell and tube heat exchanger (STHE) was selected for design and Inconel 718 was selected as material of construction to handle high temperature. Gas flow was found to be highly dilute in terms of dust concentration, so possible problems associated with dust was assumed to be negligible for design condition. Study of STHE for 2 different structures (1-2 STHE and 2-4 STHE) along with variation in internal tube diameter and number of STHE in parallel was done. Thermal study of STHE was done by utilizing Kern’s method and cost analysis was done using capacity factor method and detailed factor method. Centrifugal radial fan and turbo blower was selected as pressure compensation equipment. Cases with inability to use both equipment was assumed to be technically infeasible. Economic feasibility was studied by calculating NPV. NPV was calculated based on total installed cost and energy savings from STHE. Study of weight, size and footprint of STHE was performed. Sensitivity analysis of NPV with equal percentage variation and more realistic variation of STHE design parameters was also done. The project was found to be both technically and economically feasible. Heat duty was 7.6 MW for 1-2 STHE and 10 MW for 2-4 STHE. Placing 8 STHE in parallel gave almost negligible energy loss from pressure drop. NPV varied between -167 MNOK and 25.2 MNOK for different test cases. Internal tube diameter of 0.051m gave highest NPVs. Highest NPV for 1-2 STHE structure was 25.2 MNOK and was found by placing 2 STHE in parallel. Highest NPV for 2-4 STHE structure was 24.59 MNOK and was found by placing 3 STHE in parallel. Cost of electricity gave highest sensitivity for real case scenario while inlet temperature of CO2 gave highest sensitivity for equal percentage variation