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Plants and Equipment
Published in Carl Bozzuto, Boiler Operator's Handbook, 2021
An economizer traps heat by transferring energy from the flue gas to the boiler feed water. That heat does not leave the boiler but is returned to the system. Economizers are normally found in higher pressure steam plants. On most low pressure or any of the HTHW plants, the gas temperature leaving the boiler is already fairly low. The surface area of an economizer would be quite large (small temperature difference), making the device quite costly to recover very little additional heat. Some higher pressure plants do not benefit from the addition of an economizer as well. An economizer can work in a low pressure steam plant that has no condensate returns. There, the feed water temperature would be much lower than steam temperature. If there is a low pressure plant, with little condensate returns, such that the feed water temperature (before heating in a feed tank) would be around 100°F lower than the steam temperature, an economizer could be used to trap some of the energy lost up the stack.
Plants and Equipment
Published in Kenneth E. Heselton, Boiler Operator’s Handbook, 2020
When the boiler feedwater is colder than the steam and water in the boiler, it can extract more heat from the flue gas. Fluids colder than what’s in the boiler can also be used in an economizer to recover the heat. An economizer on a high pressure boiler plant makes it as efficient as low pressure boilers because the feedwater supplied to the economizer inlet is about the same temperature as steam and water in a low pressure boiler. It’s important to be certain the feedwater flows through the economizer in the opposite direction of the flue gas so it sees hotter flue gas as it heats up and the coldest water is exposed to the gas just before it leaves the economizer. Economizers can heat feedwater to a higher temperature than the flue gas leaving the economizer because of the counterflow arrangement.
Evaluation of the Ventilation System
Published in David W. Bearg, Indoor Air Quality and HVAC Systems, 2019
Another design approach for controlling the OA quantity entering the HVAC equipment is called “economizer control,” where the OA quantity can increase as a function of the outdoor air temperature and thereby provide “free cooling.” There are two types of economizer systems: temperature economizer and enthalpy economizer. With temperature-based economizers, the OA quantity to be introduced is based on the dry-bulb, or sensible, temperature of the OA stream. Typically, this latter system operates with an outdoor air control regime based on achieving a constant mixed air temperature. In this control regime, if the outdoor air temperature is below a high-temperature limit, typically anywhere between 65°F and the temperature of the return air (RA) stream, the return, exhaust, and OA dampers (see Figure 5.2) modulate to maintain a mixed air temperature close to the desired delivery temperature for the building. There will, of course, be a temperature rise of a few degrees as the mixed air passes by the supply air fan, picks up heat from the fan motor, and becomes the supply air. When the outdoor air temperature exceeds the high-temperature limit setpoint, the OA damper reverts to its fixed minimum position and the return air damper goes to full open.
A comprehensive review on organic Rankine cycle systems used as waste heat recovery technologies for marine applications
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2022
Olgun Konur, C. Ozgur Colpan, Omur Y. Saatcioglu
Exhaust gas economizer systems are very common applications for WHR in ships. An exhaust gas economizer transfers the exhaust gas waste heat of the engine through feed water by a shell-and-tube type heat exchanger that is placed on the main engine funnel. The feed water in the economizer drum boils and forms pressurized steam, thus transforming the exhaust gas waste heat into useful work by using the produced steam into different sections of the ship’s steam service system such as heating the fuel tanks and circuits, adjusting the oil/fuel separation temperature, meeting the heating demand of the bilge separator and hot water supply. However, the heat demand of the ship is relatively small compared to the heat released from the exhaust of the engine (Baldi and Gabrielii 2015). In this point of view, steam turbines are proposed for WHR in marine vessels but the applications have been limited to large vessels (main engine power of over 25 MW) (MAN Diesel & Turbo 2014a). The steam production process in marine vessels takes place in a closed-loop circuit. Boiler plants generally emit the exhaust gas in the temperature range of 180–220°C (Baldi, Larsen, and Gabrielii 2015). The temperatures below these ranges increase the risk of low-temperature corrosion on engine parts and pipelines due to the increased sulphuric acid production (Choi and Kim 2013). It means that only the high-temperature exhaust gas waste heat is utilized for steam production. The remaining exhaust gases contain medium- or low-grade waste heat that cannot be utilized for the process, which is potentially suitable for utilization with a suitable WHR technology-like ORCs.
Reigning in on Data Center Energy Efficiency
Published in Energy Engineering, 2018
Shrenik Ajmera, Tejas Desai, Frank Morrison
Air-side economizers can operate in both partial (integrated) or full economizer mode. In the former case they help to reduce the load on the primary cooling system and in the latter case they completely replace the operation of the primary cooling system. Transitions into and out of economization must be handled properly to avoid interruptions to cooling of the data center.