An Improved Heating System with Waste Pressure Utilization in a Combined Heat and Power Unit

Abstract

An improved heating system integrated with waste pressure utilization (WPU) for combined heat and power (CHP) cogeneration was proposed. The new heating system efficiently utilized the excess pressure of the extraction heating steam to drive the WPU turbine and generator for producing electricity, achieving higher energy efficiency and lower fuel consumption of the CHP unit. The results of the detailed thermodynamic analysis showed that applying the proposed concept in a typical 300 MW coal-fired CHP unit could reduce the standard coal consumption rate by 9.84 g/(kW•h), with a thermal efficiency improvement of 1.97% (absolute value). Compared to that of the original heating process, the energy efficiency of the proposed process decreased by 0.55% (absolute value), but its exergy efficiency increased dramatically by 17.97% (absolute value), which meant that the proposed configuration could make better use of the steam energy and contribute to the better performance of the CHP unit. As the unit generation load and supply and return-water temperatures declined and the unit heating load rose, the WPU system would generate more electricity and its energy-saving benefit would be enhanced. This work provides a promising approach to further advance the CHP technology and district heating systems.

Modeling and Off-Design Performance Analysis of a Screw Expander-Based Steam Pressure Energy Recovery System in a Combined Heat and Power Unit

“…In regular CHP units, the fifth stage of extraction steam is generally adopted for heating the supply water in the heater for the heating network (HHN), that is, the extraction port is arranged on the connecting pipe between the intermediate-pressure (IP) and low-pressure (LP) cylinders of a steam turbine. 19 The exhaust pressure of the IP cylinder generally ranges from 0.2∼0.5 MPa, where the extraction steam is sent to the HHN to heat the return water, and the designed supply-water temperature is approximately 130 °C. Because of climate change and energy-saving technology in building construction, the actual supply-water temperature is approximately 90 °C, 20 and the HHN can meet the heat exchange demand when the terminal temperature difference is approximately 10 °C.…”

“…The steam pressure energy recovery principle is similar to that of gas pressure energy recovery, and there are many application scenarios in industry and commercial processes. − This paper focuses on the pressure energy recovery in the heating pipeline of a combined heat and power (CHP) unit. In regular CHP units, the fifth stage of extraction steam is generally adopted for heating the supply water in the heater for the heating network (HHN), that is, the extraction port is arranged on the connecting pipe between the intermediate-pressure (IP) and low-pressure (LP) cylinders of a steam turbine . The exhaust pressure of the IP cylinder generally ranges from 0.2∼0.5 MPa, where the extraction steam is sent to the HHN to heat the return water, and the designed supply-water temperature is approximately 130 °C.…”

“…Using an expander, the extraction steam can heat the return water in the HHN after being used for power generation. Some work has been carried on the overall performance of the expander-based heating system. , The expander efficiency is normally assumed as constant for system performance estimation, which is plausible for a system operating at a stead point. However, a CHP unit often works under off-design conditions due to the variations of the load.…”

Modified High Back-Pressure Heating System Integrated with Raw Coal Pre-Drying in Combined Heat and Power Unit

“…The waste heat recovery of exhaust steam for CHP has been the focus of a great deal of research in the last decade [14][15][16]. Diminishing the return-water temperature of the primary heating network is an efficient method to utilize the energy of the exhaust steam by heating the low-temperature return-water [17].…”

The Significance of a Building’s Energy Consumption Profiles for the Optimum Sizing of a Combined Heat and Power (CHP) System—A Case Study for a Student Residence Hall

“…CHP systems generate heat and electricity simultaneously by burning a single fuel source and are nearly 30-40% efficient compared to the conventional systems [4][5][6]. Due to their onsite installation and use of their waste heat, the losses from CHP systems are 16-25% lower than those from the conventional systems, which use two different sources to meet the buildings electrical and thermal demands.…”