Heat transport analysis in a district heating system applying waste heat from GTHTR300, a commercial design of high-temperature gas-cooled reactor

Abstract

A district heating system for household heating and road snow melting utilizing waste heat from Gas Turbine High-Temperature Reactors of 300 MW (GTHTR300s), a high-temperature gas-cooled reactor design, was analyzed. The application area was set in Sapporo and Ishikari, cities with heavy snowfall in northern Japan. The heat transport analyses were performed by modeling heat-transfer components in the system to estimate the system's overall heat supply profile. These components included the pipelines of the secondary water loops between the GTHTR300s and the heat-application area; heat exchangers to transfer the heat from the secondary loops to the tertiary water loops of the district-heating pipes; and the district-heating pipes of the tertiary loops between the heat exchangers and houses and roads. Single- and double-pipes for the secondary loops were compared. Although the double-pipes were advantageous for having less heat loss and a smaller excavation area, these advantages did not compensate for the higher construction cost of the pipes. To satisfy the heat demand of the application area in the month of maximum requirement, 520-529 MW of heat were supplied by 3 GTHTR300s and delivered by 6 secondary loops, 3,450 heat exchangers about 90 m long, and 3,450 tertiary loops. More efficient designs for the heat exchangers and improvements to the tertiary loops applying branched flow networks are desired to reduce the number of heat exchangers and tertiary loops and to make the heat exchangers smaller. Heat lost to the ground from the tertiary loops comprised 80%-90% of the heat loss. Applications of the larger pipe or loops using the branched flow network or double-pipe are required for more efficient heat utilization. More than 90% of the construction cost went into thermal insulators. The thickness and properties of the insulator must be reevaluated for economical heat delivery.

Keywords

• high-temperature gas-cooled reactor
• gthtr300
• waste heat application
• district heating
• heat-transfer modeling