Return Water Research Articles

Combined heat and water system for long-distance heat transportation

Chinese district heating systems are transforming to clean heating systems. The excess heat in CHP and industrial plants are expected to play a dominant role in the transformation considering their enormous heating potential. As excess heat sources usually locate distant from heat demand center, efficient transportation technologies are required. In this paper, combine heat and water (CHW) system was proposed for long-distance heat transportation, using water in water supply system as heat carrier. The CHW system gives heat a free ride to urban area, no needing return water pipeline; thus, it can sharply reduce the costs of transportation. According to investigation, the application prospect of CHW was found in Northern China. A CHW system scheme combing seawater desalination system and excess heat heating system was introduced. Furthermore, through a case study in Xiongan new area, the energy efficiency and economic cost were analyzed. The proposed CHW system can provide 1500 MW heating capacity and 100 million m3 annual water supply quantity. The efficiency of heating with the CHW system is equivalent to a heat pump with COP at 6.74, even the transportation distance is over 200 km. The CHW system has significant advantages in long-distance heat transportation.

Full-scale operation of a novel two-pipe active beam system for simultaneous heating and cooling of office buildings

This paper presents an investigation on the operation of a novel active beam system installed in an office building located in Jönköping, Sweden. The system consists of two parts: a dedicated outdoor air system (DOAS) to satisfy latent loads and ventilation requirements, and a water circuit to meet sensible heating and cooling loads. The novelty of the system is in relation to the water circuit, which is able to provide simultaneous heating and cooling through a single water loop that is near the room temperature. The energy performance of the system is currently being monitored through a number of sensors placed along the water circuit. Relevant physical parameters are being measured and data are available through a monitoring system. A preliminary analysis shows that the system is performing as designed. Results are shown for a typical week in winter, spring and summer. In particular, the supply water temperature in the circuit was between 20°C (in summer) and 23.2°C (in winter). The maximum supply/return temperature difference was found in summer and it assumed a value of 1.5 K. It is noticed that in spring supply and return water temperatures almost overlap.

О РЕАЛИЗАЦИИ КАНАЛА ОБРАТНОЙ СВЯЗИ В СИСТЕМАХ АВТОМАТИЧЕСКОГО УПРАВЛЕНИЯ ОТОПЛЕНИЕМ ЗДАНИЙ

The problem of determining the internal air temperature while constructing feedback control heating systems of buildings is considered. The methods of solving this problem known in the literature are analyzed. It is indicated that neither the method of representative point (points), nor wired and wireless multi-sensor networks, nor the physical model method, nor the temperature ventilation passage method can be considered sufficiently suitable for determining the average internal air temperature of a building. The problem requires further study and development. Fairly simple methods for determining this variable are proposed in the work. The main point of these methods is that the return water temperature contains information about all the variables affecting the heat consumption, including the information about the internal air temperature; therefore, through applying a model of heat exchange, it is possible to estimate the internal air temperature using the return water temperature data. In this case, it is only necessary to properly adjust the heat exchange model to the experimental data (for a specific building). To gain the necessary result, it is necessary to measure the coolant flow mass for the entire heating system, as well as the external air temperature, the direct and return water temperature in one of the cases. In the other case, it is not necessary to measure the external air temperature, since somewhat different heat exchange correlations are considered. An equation adjusted as to the experimental data is produced, which can be used to control the internal air temperature of a building in an automatic control loop. It is shown that the parametric identification quality used to control the heat exchange model is sufficiently high.

Research on Power Dispatching Modes Based on the Thermal Performance of District Heating System

Recently in winter, there appears serious wind abandoning problem in “Three North” (Northeast, Northwest and North China) regions, and the peak regulation become much more difficult in electric power grid system. So the operation mode of cogeneration for electric peak-load regulation is discussed without energy storage system, which will lead to the fluctuation of heating load and the fluctuation of supply water temperature. In this article, two different power dispatching modes are put forward and the influence is analyzed. From the simulation result, the indoor air temperature amplitudes of the two modes just have slightly different. Return water temperature amplitude of the mode II is obviously smaller than mode I. Compared with the real-time power load of Beijing-Tianjin-Hebei Region, mode II is smoother than mode I, and the difference between real-time load and dispatching load of mode II is smaller than that of mode I.

Efficiency of using heat pumps with various refrigerants in real steam turbine power units with PT-80 and T-250 turbines

Prospects for increasing the efficiency of heat and electric energy-generation and heat-and-power supply at thermal power plants obviously draw attention to such modern and innovative technologies as heat pumps. Heat pumps allow efficient redistribution of energy flows. The abundance of low-potential heat carriers and heat sources in the cycle arrangement of the thermal power plants operation requires modernization of production and increase of the fuel heat utilization factor, therefore, reduction of specific fuel consumption for the production of heat and electricity. This paper analyzes the influence and practicability of introducing heat pumps into the heating circuit of the return water of the heat network of power units with PT-80 and T-250 turbines. Heat pumps of various configurations provide invariant energy conversion factor and efficiency. To assess energy and economic efficiency, modeling of the operation of power units and calculation of heat pump circuits for various refrigerants are performed. The economic effect is represented in quarterly cash savings of operating costs.

Problems of energy efficiency of heat supply systems

The main task of energy-efficient heat supply is to ensure full compliance between the produced and consumed thermal power, subject to a minimum of reduced costs. To achieve this goal, various methods of central and local regulation are applied. Analysis of the thermal schemes of some cities in Russia showed that most of the heat sources of centralized heat supply systems are not able to support the design hightemperature graphs with central regulation. Therefore, the area of centralized qualitative method of regulation of heat load has decreased substantially. A perspective direction for the further development of heat supply systems is to appeal to the experience of foreign countries, i.e. the use of qualitative-quantitative and quantitative methods of central regulation and low-temperature heat supply. There is also an acute problem of the complete use of heat by consumers, since overstating of the temperature of the return water substantially reduces the efficiency of heat sources. A new formula has been obtained which makes it possible to predict the temperature of the return network water in variable operating modes of heating points. The resulting formula can be used to set up programmable regulators and will allow correcting irrational modes of operation of heat supply systems.

Water fluxes of Nenjiang River Basin with ecological network analysis: Conflict and coordination between agricultural development and wetland restoration

With population growth and the rapid development of society and the economy, the excessive exploitation of water resources has not only aggravated the mismatch between water supply and water demand, but also caused the deterioration of ecological water environments, particularly wetland systems. Previous research efforts have analyzed the contradictions between supply and demand in the Nenjiang River Basin, but the water resource system needs further research to identify the relationship between the internal nodes and the changes of the wetland hydrological relationship. It is necessary to establish a systematic network model to evaluate the structure and functional attributes of water resources at the basin scale, and to balance water resource utilization and wetland protection. We established an ecological network representing the water resource system in the Nenjiang River Basin, studied the changes in the system-level network configurations from 2007 to 2015, and analyzed multiple scenarios. This method also reflects the impact of human activities on wetland hydrology and water resources. The results show that the structural efficiency of the water network in the Nenjiang River Basin has been declining, redundancy has increased, and the contradiction between water supply and water demand has become increasingly serious. Agricultural recession flow is the main consumer of water resources; furthermore, the wetland has high control intensity over the system. A water conservancy project changed the eco-hydrological relationship between wetlands and other hydrological units, which led to the degradation of the ecosystem and also affected the robustness of the system. Agricultural return water is an important water supplement source for wetlands, but the duration and amount of the supplement cannot reliably meet the wetlands’ ecological needs. Finally, based on the research findings, the construction of the National Wetland Park is facilitating wetland conservation. Overall, the model results provide a scientific basis for water resource and wetland ecological restoration, so as to strengthen the sustainable management of resources.

Thermoeconomic analysis of optimization potential for CO 2 vapor compression cycle: From transcritical to supercritical operation for waste heat recovery from the steam condenser

Recent research has been focused on the utilization of low-grade waste heat, and the industrial high-temperature heat pump can be an alternative technology because of its simplicity and outstanding performance. However, the use of carbon dioxide in vapor compression heat pumps with high-temperature heat source is still to be optimized because of low critical temperature. In the present study, a system for waste heat recovery from the steam condenser using CO2 vapor compression cycle is modeled from the energetic, exergetic, and economic perspectives, and optimized system performances are obtained by dual-objective Jaya algorithm. Potential optimized operating strategies for transcritical cycle are discussed by the parametric study and T-s diagrams. The transcritical and supercritical cycles are further compared with each other considering different steam temperatures. The optimization strategies of transcritical cycle are based on the main purpose to improve the evaporation potential and achieve transcritical cycles with the critical point inside the closed region surrounded by the process curves, so lower superheating degree and minimum temperature difference of gas cooler, higher evaporating temperature, and more return water cooling should be employed in order to promote the cycle performances. In comparison with transcritical cycles performances, the supercritical operation shows superior performances, which are less sensitive to the variations of return water temperature.

Determination of thermal pollution of water resources caused by Neka power plant through processing satellite imagery

Given the vastness of the environment, modern methods for its monitoring its behavior and changes are of great importance. The Neka power plant uses the Caspian Sea to cool its machines, and then the return water is discharged directly from the power plant into the sea. So far, no precise, economical method has been provided for detecting thermal pollution in marine resources in the previous studies. Therefore, this paper proposes a method for detection of thermal pollution through remote sensing and satellite imagery. Landsat 8 can calculate the water temperature with the OLI and TIRS sensors. In this study, the water temperature around the Neka power plant was calculated at the eastern channel (the water inlet channel from the sea to the power plant) and the western channel (the water outlet channel from the power plant to the sea) in two different images using the separate window algorithm in MATLAB. The results indicated an increase in the temperature in the western channel. For the western channel, the mean and highest temperatures on May 26, 2015, were 292.7 K and 294.3 K and were 300.5 K and 303.4 K on April 10, 2016. Based on the results, this can have environmental impacts due to water thermal pollution.

Waste heat recovery of power plant with large scale serial absorption heat pumps

Large amount of waste heat is dissipated in industries, resulting in energy waste and environment pollution. Waste heat recovery with absorption heat pump is one of the attractive solutions. In this paper, we present the theoretical study and test of a power plant waste heat recovery system with large scale LiBr-water absorption heat pumps for district heating. Waste heat from steam condenser with temperature of ∼35 °C is recovered by the absorption heat pumps driven by steam with pressure of ∼0.25 MPa from the turbine. Heat output from the absorption heat pumps is used to preheat the return water of district heating network from ∼45 °C to ∼80 °C. The return water is further heated by the steam to ∼105 °C for heating supply. Large temperature lift of the return water is achieved by the serial absorption heat pumps. Theoretical analysis of the system is presented, showing advantages compared to the conventional absorption heat pump and original heating supply system. On-site test showed that COP of 1.77 and heating capacity of 63.57 MW were achieved by one serial absorption heat pump, with waste heat inlet/outlet temperature of 34.63/28.33 °C and return water inlet/outlet temperature of 45.94/81.34 °C.

Operation optimization of heat pump in compound heating system

There are many problems of central heating system in China: low efficiency, inadequate regulation function, serious thermal imbalance and excessive heating. Due to these problems, energy-saving work of central heating system is particularly important. The operation strategy of the heating system and the accurate adaption of heating demand will directly affect the energy consumption. Based on the heating load, the corresponding heat supply system and the specific equipment are established into a mathematical model, and the operation characteristics of the compound heating system is optimized by genetic algorithm.The result shows that the heating load ratio of heat pump units increases gradually with the increase of outdoor temperature, when the outdoor temperature is higher than 5℃, the heat pump units bears the heat load alone in Qingdao city. Its COP is affected by outdoor temperature and partial load rate. The steam consumption is related to the supply and return water temperature of the network. We propose a method to achieve the lowest operating cost of compound heating system by optimizing the supply and return water temperature and circulating water flow. Optimization result contains reasonable supply and return water temperature, appropriate load bearing ratio of heat pump units, which can effectively reduce the steam consumption. Compound energy system can improve the matching relation between heat supply and heating load, because the heat pump connected to the secondary network can improve the supply and return water temperature. Heat pump units will save 20% to 30% of operating cost when heating alone.

Optimization of circulating cooling water networks considering the constraint of return water temperature

Circulating cooling water system is widely used in industry. Traditionally, circulating cooling water system is in a parallel structure. Without reuse of cooling water, the return temperature of water is low and total flow rate of water is high. This leads to the low efficiency of cooling tower and high energy consumption of system. When the coolers are in series arrangement and water is reused, the return temperature of cooling water will increase. High return temperature of cooling water can lead to the severe fouling of coolers. The level of fouling depends on outlet temperature and velocity of water. In this paper, we proposed model where cooling water is reused and the fouling of cooler is avoided. The numerical relationship between stream velocity and return temperature is introduced. The objective is to formulate the framework with minimum flow rate and no fouling with coolers. A case study is used to show the effectiveness of the proposed model.

Experimental investigation on vapor-pump equipped gas boiler for flue gas heat recovery

To recycle the flue gas waste heat, a vapor-pump system is built and its performance is fully discussed in this paper. The vapor-pump system consists of a gas condenser, an air humidifier and a gas-water heat exchanger. The boiler oxidizing air is heated and humidified in the air humidifier. Thus the dew point of the boiler outlet flue gas is improved to above 60 °C. Then in the gas-water heat exchanger, the waste heat is recovered by the heating network return water. According to the experiment results, the exhaust flue gas temperature is reduced from 80–30.9 °C. The system efficiency improvement reaches over 10%. The return water temperature, the ambient air wet bulb temperature and the circulation water mass flow rate affect the system performance markedly. The system performance changes during a whole winter are simulated. Besides of energy saving, the vapor-pump system also can reduce the pollutant emission concentration. If the air is heated to over 50 °C, the concentration of NOx decreases from 33–24.6 ppm, the reduction is about 25.4%. The vapor-pump system achieves energy saving and emission reduction simultaneously. Techno-economic analysis is also proposed in this paper, the payback period is only 0.7 year.

Shielding activated return water at the ESS

ESS utilises water both for moderating neutrons to thermal energies, as well as to cool beryllium- and steel reflectors, the shielding and plugs. This means that the water, in separate loops, will be subject to a significant proton and neutron irradiation causing the water to activate. After irradiation, the water is led to delay tanks situated inside the target building. Before returned to the target monolith ∼ 10% is led to the ion exchanger.This paper aims at determining the shielding required to ensure that the biological dose-rate requirements in the target building and neighbouring instrument halls are met during operation of facility.

Water quality effects on flotation: Impacts and control of residual xanthates

For increasing the sustainability and cost effectiveness of their operations Boliden Kevitsa Mining Oy in collaboration with academic research partners aims to develop a holistic approach to water management in its mineral processing operation. This paper describes one of the first steps taken in this process, namely the monitoring and control of residual collectors in their flotation circuits.Boliden Kevitsa Mining Oy, a Cu-Ni-PGE concentrator recycles 90–95% of its water for use in the plant. The quality of recycled water tends to deteriorate as various elements and compounds such as Ca, Na, Mg, K, SO42− and residual reagents accumulate. The accumulation shows seasonal cyclic variation that has an impact on flotation performance.UV/VIS Spectrophotometry was employed to measure residual xanthates in key process streams and process return water from the Tailings Storage Facility. This allowed the implementation of dosage monitoring and control strategy with the objective of performance control and optimization throughout the seasonal changes during the year.

Experimental and theoretical investigation of a novel full-open absorption heat pump applied to district heating by recovering waste heat of flue gas

The industrial exhaust flue gas contains tremendous waste heat that cannot be efficiently recovered by conventional condensing heat exchanger. This paper proposes a novel full-open absorption heat pump for the total heat recovery of flue gas. The recovered heat is used for district heating. By applying direct-contact heat and mass transfer without solid transfer interfaces, the novel system can save considerable metallic tube or plate materials and therefore the initial investment can be reduced substantially. A prototype full-open absorption heat pump is developed and tested, achieving the COP (coefficient of performance) of 1.621 and the exit flue gas dew point of 36.2 °C at most. A detailed theoretical model in Eulerian–Lagrangian formulation is established, involving in conjugate heat and mass transfer and particle dynamics. The numerical simulation agrees well with the experiment results. On the basis of the validated model, three critical parameters, including excess air coefficient of the burner, moisture content of the objective flue gas and return water temperature of the district heating network, are selected to study their effects on system performances. As a controlled variable, especially, the excess air coefficient plays an important role by influencing the regeneration of the liquid absorbent in the generator. The full-open absorption heat pump outperforms the condensing heat exchanger by 19.7–178.1% in heat recovery capacity as the return water temperature increases from 40 to 55 °C.

The evaluation of the optimal medium temperature in a space heating used transcritical air-source CO2 heat pump with an R134a subcooling device

In this study, a space heating used transcritical CO2 heat pump system with an R134a subcooling device was proposed and the medium temperature was researched theoretically and experimentally. To validating the existence of the optimal medium temperature, the system performances were studied: the system power dissipation declined, while the heating capacity increased first and then decreased with the augment in medium temperature. To search the reason of the optimal medium temperature, the system parameters of both the refrigerant side and water side were also discussed in detail: the varied trend of the parameters were sophisticated with the change in medium temperature. Additionally, a correlation was established to predict the optimal value of the medium temperature under various conditions with the ambient temperature, water return temperature and water delivery temperature as the independent variables.

Radiation challenges of primary cooling return water at the ESS

At ESS water is used both as thermal moderators and to cool the beryllium- and steel reflectors, the shielding and plugs. This means that the water, in separate loops, will be subject to a significant proton and neutron irradiation which will activate the water. After irradiation, the water is led to delay tanks situated in one of the triangular rooms downstream from the target. This paper aims at determining the shielding required to ensure that the biological dose-rate requirements in the target building and instrument halls are met during operation of facility.

Conjugate heat and mass transfer study of a new open-cycle absorption heat pump applied to total heat recovery of flue gas

Industrial exhaust flue gas contains massive heat and water. Effective recovery will make positive sense for energy saving and conservation. Traditional condensing heat exchanger is restricted by coolant water temperature and corrosion problem. This paper proposes a new open absorption heat pump (OAHP). The system works on the basis of directly contacting spray heat and mass transfer occurring in three main parts, including generator, condenser and absorber. Driven by high-temperature flue gas directly from a burner, the system generates strongly concentrated LiBr solution prepared for the absorption of moisture and heat from the objective flue gas. A detailed theoretical model is established in Eulerian-Lagrangian formulation to simulate the particle dynamics and the heat and mass transfer characteristics. Extraordinary temperature profiles different from those in common heat transfer are found in the generator and are explained by the conjugate heat and mass transfer. The effects of the driving flue gas temperature and the return water temperature on system performances are studied. The OAHP system achieves excellent heat recovery capacity even at high return water temperature, indicating superiority to the condensing heat exchanger.

Modular simulation of cogeneration system based on absorption heat exchange (Co-ah)

Restricted by the return water temperature of district heating network, conventional cogeneration plants cannot efficiently recover the low-grade waste heat of exhaust steam. A novel cogeneration technology based on absorption heat exchange (Co-ah) has been successfully applied to waste heat recovery of thermal power plants, enlarging the heating capacity of district heating network. In this paper, a modular simulation code is developed to simulate and analyze the complicated Co-ah system. The establishment and solution of system equations are accomplished automatically, so any changes in operating conditions or system configuration can be easily dealt with. The theoretical models are validated by the practical operating data. A comparison between the conventional cogeneration system and Co-ah system is made. With the help of the absorption heat pump, the Co-ah system recovers more waste heat from the exhaust steam and exhibits better exergetic and economic performances than the conventional system. The effects of three key parameters including back pressure, extract flow rate and extract pressure on cogeneration performances are analyzed in details, providing a guide for regulation strategies when operating conditions vary.