Cogeneration is the simultaneous production of electrical and thermal energy resulting from maximum use of primary energy (natural gas or biogas) through systems that ensure maximum energy efficiency and instead of releasing into the environment, recover and enhance heat produced by an endothermic engine (or turbine).
Producing electrical energy by a cogeneration system is very advantageous compared to simply purchasing energy; furthermore, it allows to make maximum use of heat generated by engine cooling processes: hot water can be released directly into the production cycle and used to warm up work areas, while the high heat generated by exhaust fumes can be used to generate steam or heated water, to warm up the diathermic oil, or for other needs.
Cogeneration reduces energy costs up to 30% and improves the public image of companies and factories. Furthermore, it contributes to creating an environmentally sustainable system that is in synch with European and national directives, as well as global objectives aimed at safeguarding the environment.
We define trigeneration as a form of cogeneration that combines the production of electrical and thermal energy with cooling energy: a system that uses heated air and engine exhaust fumes (or steam generated by the fumes) to generate cool water at the desired temperature. Trigeneration enables all produced energy to be made full use of by generating cool water both for industrial processes and to cool equipment and machinery.
It is a primary energy source, primarily of fossil origins. Natural gas is a a combustible mix of gaseous substances (comprising of hydrocarbons and non-hydrocarbons). Hydrocarbons include methane, ethane, propane, and butane gas, while non-hydrocarbons include primarily carbon dioxide, nitrogen oxides, and sulphur oxides. Natural gas accumulates in self-contained underground deposits, where the rocks are porous and impermeable rocks above trap the gas and stop it from escaping towards the surface.
Cogeneration, which is also referred to with the acronym CHP (Combined Heat and Power), is the simultaneous or consecutive production of two different forms of energy, mechanical and thermal, generated by a single primary energy source and a single integrated system. CHP systems generally comprise of a primary system, a generator, a heat recovery system, and electrical interconnections — all parts of a single integrated system. Cogeneration relies upon recovering heat generated during electrical energy production, which would be otherwise lost, reusing it to produce thermal energy. Cogeneration must therefore be considered a plant solution which increases the efficiency of energy production.
Below is a list of the advantages of cogeneration: – greater energy conversion efficiency;
– reduction of polluting emissions, in particular, greenhouse gases, such as carbon dioxide; – worthwhile payback benefits, thanks to current legislation that allows tax exemptions for use of natural gas;
– decentralization of energy production, avoiding inevitable losses due to long-distance transport;
– employment of a strategy which adequately covers energy needs, whilst also preventing possible black-outs and network malfunctions;
– valid vehicle for the promotion and incentivization of a de-monopolized energy market.
CHP systems allow the emission of greenhouse gases to be substantially reduced: in more detail, each kWh produced by a methane gas cogeneration system saves about 450 g of CO2 being released into the atmosphere, compared to when electrical and thermal energy is produced separately. This, in essence, results in a 43% reduction of carbon dioxide emissions. Furthermore, mitigation of adverse environmental impact is also as a result of the reduction of NOx and SOx being produced.
One of the disadvantages of the CHP system is the substantial financial investment it requires. However, there is no doubt that it can also represent a new resource for companies and factories to be considered when wanting to consolidate specific and innovative professional profiles. Furthermore, cogeneration and its intrinsic capacity to produce energy locally are becoming one of the major supporters of local economic growth.
A maximum percentage value can be quantified around 30%, with returns on investments to be expected after 2 to 4 years. These performance values are to be evaluated in the context of three primary variables: the size of the factory/plant, effective thermal recovery, and hours of operation per year.
The choice of the best technological partner is, therefore, essential for a successful outcome of the project. Feasibility studies, excellent products and efficient maintenance services are the basic ingredients for energy efficiency and, therefore, savings.
The administrative procedure is the following: – PROVINCIAL REQUIREMENT: it is necessary to get Single Authorization for the system; this request may require 6 to 8 months to be processed after submission.
– ENEL REQUIREMENT: it is necessary to sign a contract to be connected to the primary electricity distribution network; this request may take approximately 2 to 3 months to be processed after submission.
– FIRE MARSHAL REQUIREMENT: it is necessary for a Fire Marshal to inspect the system to ensure compliance with safety standards and to issue a CPI (Fire Prevention Certificate) Certification.
– UTF (Finance Technical Office) REQUIREMENT: it is necessary to request a license to produce and sell energy; this procedure must take place during the installation of the system and must be completed prior to system testing.
– DIA (Declaration of Commencement of Activities): it is necessary to obtain building authorization and permits.
“White Certiticates”, more aptly called TEEs (Titles of Energy Efficiency) represent an incentive system for the installation of efficient technology and systems.
One certification corresponds to saving one ton of petroleum. The certification consists in certificates that can be purchased and then sold on and whose value depends upon market trends at the time of purchase/sale. They are issued by the GME (Manager of the Electric Market), following a check of energy savings achieved, for example, by use of a cogeneration system with an endothermic engine, as compared to traditional electrical and thermal energy production systems.
White certificates concern three types of interventions:
1. Electrical energy savings;
2. Natural gas savings;
3. Savings of other combustible resources.
Assistance is a fundamental part of the cogeneration system. Let’s use the example of a system in a factory where there are three work shifts, on weekdays only, for 11 months of the year. Let’s imagine how many kilometers a car engine would accrue if it were to travel at 60 km/h, 5 days per week, for 48 weeks: 345,000 km per year. This shows that maintenance is fundamental to selecting a supplier, especially if costs associated with machinery idleness are considered. Considering that a system that uses 1000 kW at current energy costs can bring about savings of about 1500 Euros per day, we can use this to work out how costly idleness can be!
We have to consider that it may be rather difficult to manage excess energy generated by the site where the system is installed. Furthermore, energy transported from one site to the other would incur a variety of costs and expenses such as transportation, dispatchment and measurement, as well as system expenses and the fact that the same amount of energy collected has to be released to the network. Therefore, it may be more feasible to reach an agreement with a trader or relinquish it to the GSE (Administrator of Energy Services), who is compelled to collect any excess CHP energy at a set price.
No, not all methane gas is tax exempt. In order to quantify the amount of tax exempt gas, the UTF office relies upon the electric power reader installed at the alternator’s terminals, calculating consumption of 0,25 mc/kWh. Essentially, energy efficiency is rewarded.
Concerning the need for 7° water, is it possible to use a Lithium Bromide absorber; as far as the second case is concerned, an ammonia solution absorber can be used, but must be considered very carefully given the complexities and costs of using it. Other absorbers which are capable of reaching temperatures between 7° and 0° C are now emerging on the market, although these technologies require further study.
Since air is continuously renewed and collected from the outside without any thermal recovery, it is possible to simply warm up the air by use of a room temperature air/water battery that can reach the maximum temperature based upon its quantity. The steam produced by the system via exhaust fumes would integrate/replace steam produced by boilers.
Although the gas turbine produces large amounts of steam, I do not think that it is suitable in this case, as work in two shifts (15+ hours/day) does not lend itself to the use of a turbogas cogeneration system. The turbine is a machine that is best used in continuous work cycles: the start/stop process is not suitable for it and it will substantially shorten maintenance intervals. With your scenario, since you turn off the plant on a daily basis, I think that an endothermic engine system is more suitable. However, with an engine system it is also necessary to carefully evaluate whether the hot water produced by the system may be used in your factory.
Since you use a lot of non-recoverable steam, it may be wise to evaluate whether it is possible to preheat the reintegration of steam boilers with the low temperature energy produced by the engine; for any other possible use of water, it would be necessary to study your production cycle in more depth.