Industrial Energy Solutions: Piping, Cogeneration, Steam Turbines
External Network of Pipes
The optimal solution for external piping is installation in underground trenches or galleries, drawing from general industrial plants. Care must be taken to prevent frost, which can cause freezing in condensates and subsequent damage. Both condensate collectors and valves should be placed in easily inspectable boxes. External pipes should be welded and flanged for valves and separators. It is not required to insulate compressed air pipes, unless hot air is necessary; however, anti-corrosive paint should be applied on the outside. For pipes up to 50 mm, threaded connections may be used, or welded connections instead of locking couplings between coupled halves.
Cogeneration Systems
Reciprocating Engine Plants
These plants utilize gas or oil as fuel for reciprocating engines. They are highly efficient electrically but are thermally less efficient. A heat recovery system is designed according to industry requirements, generally based on the production of low-pressure steam (up to 10 bars), heating oil, and using high-temperature circuit water cooling. They are also suitable for absorption cooling production, either by steam generated from dual-purpose gas machines or directly using the heat from cooling water machines with simple operation. In heat and power cogeneration applications, the following types of reciprocating engines may be used:
Diesel Engines
These engines operate using light or heavy gas oils and employ compression ignition systems. We distinguish the following types:
Fast Diesel Engines
Feature rotation speeds between 1000 and 3000 rpm, piston diameters of 200-250 mm, cylinder power between 100 and 200 kW, and thermodynamic efficiencies from 36% to 38%.
Semi-Fast Diesel Engines
Have rotation speeds between 400 and 1000 rpm, piston diameters of 500 mm, power per cylinder of 600 to 1000 kW, and 40% thermodynamic efficiency.
Slow Diesel Engines
Have speeds between 100 and 400 rpm, piston diameters around 1000 mm, with power per cylinder from 2500 to 3000 kW, yielding a thermodynamic efficiency of 42%. They typically use two-stroke cycles.
Gas Engines
These engines operate according to the Otto cycle, burning gas fuel. Compression ignition is not used; instead, they employ one of the following systems:
- Compression of the gas-air mixture and spark ignition.
- Compression of the gas-air mixture and injecting a small amount of diesel, which, upon burning, initiates the air-gas combustion.
Modular Cogeneration Equipment (EMC)
Modular Cogeneration Equipment (EMC) is often found on the market. These are compact units, factory assembled and tested, incorporating the reciprocating engine with an electrical generator and the appropriate system for heat supply (in the form of hot water or very low-pressure steam).
Heat Recovery from Reciprocating Engines
Heat recovery in reciprocating engines can be carried out in three ways:
- Exhaust Emissions: The engine exhaust gases have temperatures of approximately 400°C. Approximately 0.45 kWh can be recovered per kWh of electricity generated.
- Engine Cooling Water: In water-cooled engines, most of the heat from the engine cooling water can be recovered, yielding 0.5 to 0.8 kWh of thermal power per kWh of electricity generated.
- Engine Lubrication Oil: A portion of the recovered heat can also be obtained from the engine lubricating oil. Overall, the heat production from an internal combustion reciprocating engine is in the range of 1 to 1.6 kWh for each kWh of electricity. This recovery provides hot water at temperatures of 80-90°C, but heated water can also be obtained at temperatures of about 110° to 115°C.
Steam Turbine Plants
In these systems, mechanical energy is generated by the expansion of high-pressure steam from a conventional boiler. The use of this turbine was a pioneering method in cogeneration. It is currently used primarily as a supplement to combined cycle plants or those using waste fuels such as biomass or waste to be incinerated. The joint application of a gas turbine and a steam turbine is called a “combined cycle.” Yields obtained with these machines are within the full range of cyclic heat engines. Steam turbines can be classified in various ways, depending on the number and type of stages, the direction of flow in the impeller, and the steam pressure at the machine’s output.