Boiler Exhaust Gas Waste Heat Recovery Alternatives Evaluation Study

Project Synopsis

Project Summary

BATCH SPECIALTY INORGANIC CHEMICAL PLANT WASTE HEAT RECOVERY ALTERNATIVES EVALUATION

The client owns and operates a facility that produces specialty metals (platinum, palladium) and catalyst washcoats.  The client contracted with Process Engineering Associates, LLC (PROCESS) to perform a technical and economic evaluation of waste heat recovery alternatives for the exhaust gas from an existing waste heat boiler (WHB).  The existing WHB is fed by the exhaust from a series of batch furnaces (7 total) within the facility.  The exhaust gases are fed to secondary and tertiary combustion chambers before entering the WHB.  The WHB generates approximately 100 psig steam for use in the plant.  The exhaust gas from the WHB must be quenched from 1500^o F to 140^o F before entering a scrubber.  The alternatives evaluation focused around recovery of the energy contained in this exhaust gas.  In addition, the client also requested that PROCESS evaluate the technical and economic feasibility of using the WHB steam to generate electricity as a potential additional cost saving measure.

Specific project tasks included the following:

• Generated a process design basis summary to define project goals, constraints, and requirements and submitted this to the client for review and comment.

• Prepared a heat and material balance (H&MB) around the existing operation using process simulation software.  This simulation and H&MB was used as the basis for the technical evaluation.  It was also used to provide the client with an estimate of the quantity of leak air egress into the system through an existing bypass stack (with a faulty valve).  This information was used during the course of the review to estimate the total energy savings associated with fixing the leak.

• Identified ten (10) potential options for recovering energy from the waste heat boiler.  These options included one or a combination of the following:
  • preheating the combustion air for the primary and secondary combustion chambers
  • preheating the boiler makeup water
  • heating hot water or deionized (DI) water for use in existing processes within the facility
  • heating air for the facility
  • generating electricity with an organic Rankine cycle (ORC) system, Kalina cycle system, or thermoelectric system
  • using the steam from the waste heat boiler to generate electricity.

• Executed a technical evaluation of the potential options.  Each of the alternatives was evaluated technically with regards to:
  • available heat sink (i.e., potential energy that can be recovered economically)
  • potential to integrate the technology into the existing process
  • proven performance of the technology
  • technical difficulties and uncertainties associated with the engineering design
  • construction and operation considerations
  • effectiveness and benefit of the technology in recovering energy
  • safety, health, and environmental considerations.

• Executed an economic evaluation of the technically-feasible options.  Five (5) of the options were considered technically feasible and were evaluated economically. Cost estimates were obtained for major equipment using vendor-specific proposals.   Total annualized capital (TAC) cost estimates were generated utilizing engineering cost factors in conjunction with the vendor quotes and site specific data for utilities, raw materials, and energy consumption.  A payback period and Internal Rate of Return (IRR) were calculated based on the client’s criteria.

PROCESS issued a final report detailing all of the above information.  The client elected to pursue additional detail design and estimating of the option to preheat the boiler makeup water to the deaerator (DA) tank.  This option had a payback period of less than 6 years with an IRR of greater than 15%.

Industry Type

• Catalyst Manufacturing

Utilized Skills

• Energy audit
• Heat recovery optimization
• Process technical & economic alternative evaluations