Heat Recovery from Reformer Flue Gas

Low level heat from the reformer flue gases going to stack can be recovered and used for the preheating of combustion air, low pressure steam production, or preheating of boiler feed water or demineralized water. For this, additional heat recovery surface area is installed in the convection zone of the reformer furnace (Christensen, 2001; Nand and Goswami, 2009). The energy savings obtained from introducing combustion air preheat are due to reduced consumption in fuel to the primary reformer.

Also, in plants that are designed to have heat recovery systems, the efficiency of heat recovery can deteriorate over time resulting in increased flue gas temperatures. In such cases, replacing the older heat recovery systems with newer and more efficient systems will provide benefits. Prevention of moisture along with sulphur compounds, and overall economics of recovering heat at comparatively lower temperatures are among the key design concerns (FAI, 2013).

Its applicability of this measure will depend on the present operating and design conditions of the plants such as available space, use of additional low level heat recovered, and integration with inlet /oulet temperatures of various process streams (FAI, 2013). Introduction of low pressure steam production or preheating of process water results in low level heat savings and is generally a simpler solution than combustion air preheating (Christensen, 2001b). 

Development Status Products
Commercial
Ammonia

Heat Recovery from Reformer Flue GasCosts & Benefits

Parent Process: Steam Reforming
Energy Savings Potential

Reducing the stack temperature by 100˚C will result in energy savings of approximately 0.4 GJ/ t NH3 (Christensen, 2001).

Indian Flag By installing a feed pre-heat coil in the low temperature convection section of the reformer flue gas duct, a plant in India was able to reduce flue gas temperature of the reformer from 170˚C to 148˚C and eliminated the need for a fired heater, resulting in energy savings of 0.17 GJ/t NH3 (Nand and Goswami, 2009). 

Indian Flag Another Indian installed a natural gas heating coil to recover the heat from the reformer flue gas. The reformer flue gas temperature was reduced from 190˚C to 160˚C, saving 0.18 GJ/t NH(Nand and Goswami, 2009). 

At an ammonia plant in Pakistan, a demineralized water preheating coil was installed to recover heat from the flue gas (240˚C). The temperature of the flue gas was lowered to 137˚C, recovering approximately 44 GJ/hour of waste heat from the flue gases (Yousaf, 2011)

CO2 Emission Reduction Potential
Costs

Heat recovery in the Pakistani plant saved $ 2 Million/year (Yousaf, 2011)

Indian Flag For a 1 300 tpd plant, the required investments are estimated to be around US $ 700 000 [2008 values] (FAI, 2013).