How It Works

An ebullient-cooled engine with an industrial steam boiler (HRSG). Steam generated within the water jacket of an engine at WOT (wide open throttle) supplements auxiliary steam previously provided by the boiler. The heat from the engine exhaust, pretreated with 3-way catalyst, provides supplemental firing of the boiler while providing inert flue gas needed for NOx reduction. Utilizing a regenerative drive, which is certified for utility interconnecting, the CHP package engine generator operates at peak efficiency with high reliability regardless of output.

Exhaust from a turbo-charged stoichiometric ebullient cooled engine generator is recuperated within an industrial boiler supplying high pressure process steam from 100% makeup water. After passing through the boiler generating steam, the combined exhaust is mixed with ammonia. The mixture of boiler and engine exhaust is passed through a selective catalytic reduction system resulting in NOx emissions less than 0.006 lbm NOx/mmbtu heat input. The boiler exhaust emission rate will be within the 0.07 lb/MW-hr rate of CARB 2007. The boiler-engine exhaust is passed through a condensing heat exchanger wherein makeup water is heated from 70F to 180F prior to entering the deareator. Steam for preheating makeup water and deareating feedwater is supplied by the engine jacket. The project demonstrates greater than 95% thermal efficiency for a net HHV heat rate of 3570 btu/kw-hr. (A typical installation with little or no makeup water will exceed 80% net thermal efficiency).

The demonstration comprising the integration of an engine generator with an industrial steam boiler provides a new cost attractive option for owners/operators of steam boilers to create carbon offsets with a substantial reduction of electrical operating cost. Using the same stack with an existing air permit, the engine generator within the boiler control volume mitigates new source review so long as the permitted emissions for the boiler or engine are not exceeded. The novel design reburns engine exhaust in the boiler burner, resulting in the reduction of NOx, oxidation of CO and hydrocarbons, the indistinguishable engine boiler exhaust treated as it flows through a downstream SCR, resulting in emissions corresponding to boiler BACT, a level less than currently required of stand-alone engine generators per CARB 2007.

The prime mover is a variant of the big block V-8 with 7th generation casting having a total displacement of 632 cubic inches. The engine is modified with a liquid overfeed forced circulation cooling system that maintains nucleate boiling heat transfer throughout the engine heads and block. By nature of nucleate cooling, the cooling design maintains near constant metal temperatures throughout alleviating thermal stresses. This allows wide open throttle, the head metal temperatures maintained at or lower than a similar engine operating at half the load cooled with 100F cooler water at 10 times the circulating water flow.

Power will be generated by a premium efficiency induction motor directly coupled to the ebullient cooled engine. The engine/induction motor speed is set by a regenerative variable frequency drive (VFD) with two active front ends. The UL1741 listed Santerno VFD converts braking torque at a rotational speed to near unity power factor 3-phase power, the amount of which is a function of the engine torque and RPM. The engine generation heat rate will be constant throughout a wide range of generation by way of the wide open throttle operation of the engine.