Emergency heat dissipation in Cogeneration and Power Generation

Power generation and cogeneration plants generate and work with high thermal energy amounts, coming from mechanical movements of electro generators, endothermic engines and turbines, supplying electric energy to a production site or for grid inlet. A cogeneration plant is a particular kind of generation system, consisting in a thermoelectric plant where the fuel feeding the endothermic motor, diesel, biodiesel, natural gas, biogas or biomass, is employed for combined heat and electricity production, in order to obtain hot water for technological use, in industrial processes or for heating purposes.

Every cogeneration and power generation plant need emergency heat dissipation systems, since if heat is not recovered and recycled (for example when heat recovery is not requested or hot water need is missing), an alternative and affordable dissipation system is necessary to maintain a constant engine working temperature and the correct thermal balance, ensuring the right working conditions of the gen set, avoiding failures and engine damages, caused by the over-heating of equipments. Usually, power generation is indeed primary focused on electrical energy production, often also in cogeneration plants, so that an emergency dissipation circuit is always requested.

In a power generation plant, whether a heat recovery system for cogeneration is applied or not, heavy amounts of heat are produced: primary fuel source in the generator transforms only a small part of its potential in electricity, usually between 40 and 45%, while the rest get lost as thermal heat. Heat can then be recovered from waste fumes, from engine and hydraulic oil cooling water, or even from aftercooler systems. Cylinder's jackets can reach 90 degrees, so that cooling water can gain quite high temperatures, but always lower than 90 degrees, and also heat recovery levels on hydraulic oil depends on the power of the overall gen set. Instead, combustion fumes can reach extremely high temperatures, higher than 400 degrees, meaning very high heat amounts to deal with, and so if heat is not reused a well conceived emergency heat dissipation system must be provided.

In order to manage the several heat sources and thermal loads, the gen set can be equipped with different thermoregulating solutions and thermal machines. An emergency heat dissipation system is essential also in a cogeneration plant, where heat is usually recovered to be employed in other applications, optimizing the primary fuel performance: in fact, if the heat recovery system is not working, when heat is not requested and the recovery cycle is excluded or inactive, an emergency heat dissipation system must be available and working to dissipate extra heat, for example using radiators and fumes by-pass.

Heat recovery in a gen set is usually achieved by a cooling cycle on engine and lubricating motor oil, and also for thermal transfer with waste fumes usually treated with a pipes heat exchanger. An emergency heat dissipation system can then be conceived using different thermoregulation solutions and thermal machines, such as Evaporative Towers, water/water Heat Exchangers and radiators and free coolers, to cool down primary engine and intercooler cooling circuit water.

An emergency heat dissipation system must be engineered considering several components, not only the heat amounts to be managed, but also geographical location of the power generation site. Depending on external air temperature, connected to plant's location latitude but also to the average season temperatures where it works, and also depending from availability of cold water feeding the thermal transfer hydraulic circuit, Evaporative towers can be the best solution, achieving heat dissipation of engine cooling water by thermal transfer with ambient air, or instead electroradiators or plate heat exchangers water/water can be preferred, absorbing exceeding and not employed heat from engines and hydraulic lubricant oil cooling water itself.