District Heating Plants Research Articles

Considering different methods of thermal utilization of municipal solid waste

The article discusses the methods of thermal utilization of municipal solid waste. The environmental burden on landfill disposal sites is reduced by waste incineration. At the same time, the production of heat energy occurs with moderately lower environmental impact. The work of an integrated district heating station was considered in the article. The influence of this installation on the environment and the features of the operation of the integrated district boiler house are considered. The study demonstrates the advantages of utilizing municipal waste at an integrated district heating plant over the method of waste incineration in a regular incineration plant.

Experimental and numerical analysis of fine particle and soot formation in a modern 100 MW pulverized biomass heating plant

The formation of soot, organic, and inorganic aerosols has a profound effect on the environmental and technological feasibility of biomass combustion. In this work, the soot and aerosol processes are examined for a modern pulverized wood-burning 100 MWth district heating plant. Experimental data was collected from two locations inside the furnace (30% and 100% thermal loads), including measurements for fine particle (PM1) number size distribution, number concentration, and chemical composition. The experiments were complemented with Computational Fluid Dynamics (CFD) simulations and Plug-Flow Reactor (PFR) modeling. The measurements and modeling are combined in a comprehensive analysis, providing fundamental understanding on the aerosol processes inside the furnace. The wood-powder combustion is efficient under both thermal loads, indicated by the low unburned carbon content in fly-ash, and the low CO, NO and soot emissions (<0.3 mg/Nm3). The fine particles consist mainly of K2SO4, and of lesser amounts of alkali salts (NaCl, KCl), and Ca and Mg compounds (oxides or sulfates). A large concentration of KOH/K2CO3 vapor may exist in the flue gas and play a significant role in the heat exchanger fouling. The applied modeling tools are shown to provide accurate estimations for the composition and formation regions of fine particles inside the industrial biomass furnaces.

Implementation of a SWOT-AHP methodology for strategic development of a district heating plant in fuzzy environment

In this paper, SWOT analysis and fuzzy Analytic Hierarchy Process (FAHP) have been employed to structure and determine the importance of all identified alternatives for developing strategic management in a local district heating plant in Serbia. Weaknesses are identified as drivers of technological slowdown in the plant. The outcome of the prioritization highlights the importance of solving challenges regarding weaknesses by relying on a variety of opportunities that emerge in the environment. The potential of restoring the equipment of the district heating plant is found to be the most important alternative for strategic development.

Temperature and flow rates dynamics in a district heating (DH) network fed by a combined heat-and-power (CHP) plant

Research focus (problem description, short background):The energy efficiency of a district heating (DH) system can be improved by fine-tuning supply and return temperatures and flow rates without need for invasive renovation of the end user heating systems. Research methods:We employ a correlation coefficient to examine the relationship between the local supply temperature and the use of heat; research relies on data hourly heat generation records from each heat generation facility in the DH system of Omsk, Russia, 2016–2017. Key research results/findings:The correlation declines the further we go from winter. Firstly, the relationship between the transition states and the outside temperature results from the relationship between external conditionings and heat parameters in DH. Secondly, both the energy consumption and the supply temperature are affected by the infrastructure, other weather conditions, and energy price; they are also highly dependent on consumer behavior, which is arbitrary, heterogeneous, and interdependent. Thirdly, the regional heating load is influenced by the characteristics of a building cluster. Although nearly all DH plants have a control system in place, we find that human factor jeopardizes the performance of such systems. Main conclusions and recommendations:To generalize these results to other systems, we emphasize that the effective diffusion coefficients and effective heat-loss coefficients are influenced by the thermal dynamics in the network and change on typical time scale (one year), hence their uncertainty. This study has produced a technique for visualizing the relationship that exists in a DH system between supply temperature and heat consumption; this technique is expected to contribute to the dynamic modeling, control, and planning of future integrated energy systems. The load profiles are dynamic; a thermal storage could be used to shift the timing of heating loads to minimize the flow through DH networks.

Design of a solar district heating system with seasonal storage in Italy

The residential sector is responsible for 26% of final energy consumption in the European Union. A key strategy to reduce household fossil fuel use is solar district heating with seasonal thermal energy storage. Although this technology has been widely applied in Northern Europe (Sweden, Denmark, and Germany), it has not been implemented in Italy. This research presents a new numerical tool, and applies it to the REPLICATE project in the Italian city of Florence, which is financed under the Horizon 2020 Smart Cities and Communities initiative. Our novel tool, which is based on a dynamic model coupled with the finite element method, has been developed to guide the design of the district heating plant and obtain a reliable estimation of performance, notably storage heat losses. The overall aim is to reduce the prediction inaccuracies that have characterized past projects. The final dynamic model is implemented in TRNSYS, and makes it possible to select the main plant parameters and define control strategies. It is linked to a detailed heat transfer model developed in COMSOL Multiphysics®, which can calculate storage heat losses and determine the optimal thickness of insulation material. Our in-depth parametric study determined the optimal volume of the hot water tank to be 3800 m3, and the size of the solar field to be 1000 m2. We also evaluated the effectiveness of the addition of a water–water heat pump. This analysis found that it is a crucial component as it can increase storage capacity and improve the performance of solar collectors by up to 124 MWh. Our results indicate that with an optimized configuration, the solar fraction of the system can reach up to 44%.

Analysis of Wood Chip Characteristics for Energy Production in Lithuania

Wood chips and logging residues currently comprise the largest share of biomass fuels used for heat generation in district heating plants and are provided by a variety of suppliers. Ash and moisture contents, as well as the calorific value, may vary considerably depending on the composition of the fuel, seasonality, location, and other factors. This paper provides the summarized results of the main characteristics of wood chip moisture and ash content and calorific value, experimentally tested for a significant range of samples. Chip samples were collected from two district heating companies and tested for a significant range of samples. Chip samples were collected from two district heating companies and tested for a 3-year period. The data on fuel chip prices were taken from the electronic wood chip trading platform. The tests were performed using standard express methods, where two sub-samples were taken and analyzed from every chip sample. It was determined that the moisture content of the wood chips varied from 35% to 45%, the calorific value from 18.4 to 19.6 MJ/kg, and the ash content from 0.5% to 4.5%. The calculated relative expanded uncertainty of the moisture content measurement was ±2.1%, of calorific value—±1.5%, and of ash—±1.0%. The repeatability of the results was estimated as the pooled standard deviation.

Adjusting heat demands using the operational data of district heating systems

The main objective of this study is to investigate variations and peak values of actual heat demand profiles in a centralized district heating (DH) network. Operational heat data is utilized to discover that almost no weather correlation exists during warm months when supply temperatures exceed 60 °C; thermal inertia of buildings affects their behavior differently in terms of needed space heating; and thermal energy storage (TES) units can be important assets for improving the performance of DH networks. To draw such concluding remarks, two approaches namely scaling design heat demand and the weighted moving average (WMA) are used. Analysis of heat demand profiles reveals that the fourth generation DH (4GDH) shows promise in the Russian context. It is also observed that the discrepancy between the projected and the actual values is 7–14% higher than average, and the variation of temperature in the supply line is 1.5 times that in the return line. Through designing TESs or DH plants using more precise heat demand data, DH operator is able to reduce the energy price by lowering infrastructure costs. By implementing WMA strategies and incorporating advanced control techniques, it is also possible to save 40%–50% energy per year, which results in lower energy fees for the end-users.

Thermal energy storage sizing for industrial waste-heat utilization in district heating: A model predictive control approach

Thermal energy storage (TES) is a key technology for enabling increased utilization of industrial waste heat in district heating. The ability of TES to equalize offsets in demand and supply depends strongly on the sizing, control and integration in a heating plant. We consider the problem of sizing TES in heating plants utilizing a varying waste-heat source. To this end, we propose a combined dynamic simulation and model predictive control approach that accounts for the dynamics and optimal control of the heating plant with TES. A case study has been carried out on a district-heating plant located in Norway, with 90% of its annual heat production being heat recovered from the off-gas from a ferrosilicon plant. We evaluate the effective peak-heating reduction with different TES sizes and the energy-to-heat-flow-ratio for the TES discharging periods as performance metrics. For the case study, our results suggest that a modest TES tank volume of 1500 m3 is sufficient to achieve a half-year peak-heating reduction of 12% and comparable performance with larger volumes. The proposed methodology constitutes a numerically tractable means of incorporating the impact of model predictive control on the sizing of TES for heating plants with time-varying waste-heat supply and demand.

Will there be the waste heat and boiler house competition in Latvia? Assessment of industrial waste heat

The research aims to develop the methodology for waste heat implementation into the district heating systems by overcoming several barriers. The waste heat from different enterprises has been identified as an important thermal energy source in smart energy systems for the heat load coverage by using heat pumps. First, waste heat potential mapping eliminates the lack of information. The authors have developed a detailed assessment of the largest enterprises, their heat production levels, and the distance to the nearest district heating plant for the Latvia case study. The approach highlights the national techno-economic potential of waste heat, which has been further used for dynamic simulation of waste heat integration into the district heating systems.When allocating the techno-economic waste heat potential with existing heat demand, it can be concluded that 83 GWh or 31% of overall waste heat could be used in DH systems. The cost-benefit analysis is performed by analyzing the main income and cost flows. The total amount of waste heat potential in the rural areas is around 38 GWh per year. Even though this amount of waste heat cannot be used in DH networks, there is potential for industrial symbiosis between several different manufacturing companies to use waste heat efficiently.

CO2 emission mitigation through fuel transition on Danish CHP and district heating plants

AbstractThe study analysed how carbon dynamics were influenced by the transition from coal or natural gas to forest biomass on a number of district heat and combined heat and power plants in Denmark. For 10 plants, we calculated the cumulative net carbon emissions over time (t) from the fuel transition (CCE(t)) and carbon payback time (CPT), a measure of the time it takes for a fuel transition to biomass to reduce the amount of carbon emitted to the atmosphere relative to a continuation of using fossil fuels. Subsequently, we derived the relative cumulative net carbon emissions (RCCE(t)), as a measure of the carbon emission savings/costs induced by the fuel transition. Finally, we performed sensitivity analyses of key parameters, with special focus on emissions from indirect/market mediated effects. For fuel transitions from coal to biomass, CPT ranged from 0 to 13 years indicating that carbon emission benefits were achieved at the latest after 13 years. Relative cumulative net carbon emissions 30 years after the fuel transition (RCCE(30)) ranged from 0.29 to 0.85 corresponding to emission savings of 15–71% relative to continued use of coal. For fuel transitions from natural gas to biomass, CPT ranged from 9 to 34 years and RCCE(30) from 0.81 to 1.03. Sensitivity analyses showed that the use of truly residual biomass (harvest residues or industrial residues with no alternative use), biomass harvest from productive forests and short transport distances are instrumental in achieving a short carbon payback time and large emission savings. The quantification of indirect or market mediated GHG emissions is controversial and uncertain. We analysed additional carbon emissions related to indirect land use change (iLUC), indirect wood use change (iWUC) and indirect fuel use change (iFUC). Including iLUC added 1–4 years, iWUC added 1–3 years and iFUC added 1 year to the mean CPT.

Heat load forecasting using adaptive temporal hierarchies

Heat load forecasts are crucial for energy operators in order to optimize the energy production at district heating plants for the coming hours. Furthermore, forecasts of heat load are needed for optimized control of the district heating network since a lower temperature reduces the heat loss, but the required heat supply at the end-users puts a lower limit on the temperature level. Consequently, improving the accuracy of heat load forecasts leads to savings and reduced heat loss by enabling improved control of the network and an optimized production schedule at the plant. This paper proposes the use of temporal hierarchies to enhance the accuracy of heat load forecasts in district heating. Usually, forecasts are only made at the temporal aggregation level that is the most important for the system. However, forecasts for multiple aggregation levels can be reconciled and lead to more accurate forecasts at essentially all aggregation levels. Here it is important that the auto- and cross-covariance between forecast errors at the different aggregation levels are taken into account. This paper suggests a novel framework using temporal hierarchies and adaptive estimation to improve heat load forecast accuracy by optimally combining forecasts from multiple aggregation levels using a reconciliation process. The weights for the reconciliation are computed using an adaptively estimated covariance matrix with a full structure, enabling the process to share time-varying information both within and between aggregation levels. The case study shows that the proposed framework improves the heat load forecast accuracy by 15% compared to commercial state-of-the-art operational forecasts.

Discounting and the Green Transition: District Heating in Denmark

Taking Aalborg as the basis for a case study, we consider the discount rates, annuity rates and costs of capital that were used in recent socio-economic and financial Net Present Value (NPV) analyses of a proposed geothermal district heating plant. While the core NPV analysis applied a real social discount rate of 4 percent, in keeping with Danish government guidance, emissions and electricity prices were based on costs of capital that differed from this rate, as did the annuity rate applied in the financial analysis of the project. While the different rates are carefully justified in each setting, we question whether there is consistency in the approach taken to intergenerational welfare across different steps of the analysis. The use of high corporate rates in some contexts potentially makes it more difficult for Green Transition projects to meet the legal requirement of being evaluated as socio-economically optimal.

St1 Deep Heat Project: Geothermal energy to the district heating network in Espoo

St1 Deep Heat Project with its two deep wells extending to 6.2 - 6.4 km depth is the world’s deepest industrial geothermal energy project. The aim is to build an EGS (enhanced geothermal system) at the depth of about 5 - 6 km. The project is a pilot aiming at exploring the technical and economic feasibility of geothermal energy in the crystalline rock conditions of Finland for production of thermal power to a district heating network. Due to the demands of the district heating, the aim is to produce hot fluid at about 100°C and re-inject it to the formation at 50°C. The 100°C goal requires to drill to about 6 km depth. The drill site is located in Espoo, next to the Fortum district heating plant on the Aalto University campus. So far (2020) the project has drilled a 2 km deep completely cored pilot hole (OTN-1), and two deep wells OTN-2 to 6.2 km and OTN-3 to 6.4 km. Hydraulic conductivity has been enhanced by hydraulic stimulation in both deep wells in 2018 and 2020. The extreme depth level sets significant challenges for drilling and hydraulic stimulation, as well as controlling of induced seismicity. At present, the project proceeds with the installation of production pumps in OTN-2 and OTN-3, and first test cross-hole pumpings are expected to start in January 2021. In the presentation we provide an insight to the project and its major achievements and challenges.

Comparative analysis of the energy efficiency of different types co-generators at large scales CHPs

The comparative engineering analysis for the following cogenerator types have been performed: eleven Jenbacher piston engines J920 (Jenbacher, 11xJ920) with an installed power capacity per engine of 9.52 MW; 2 S Gas Turbines SGT-800 (Siemens 2 x SGT-800) with an installed power capacity of each turbine of 56.35 MW; one General Electric Gas Turbine 6F.03 (GE 1 × 6F.03) with the installed power capacity of 83.05 MW. Considered variants of co-generators should replace ineffectively operating existing unit in summer mode in a large scale CHP, which includes steam boiler TGMP-344A and steam turbine T-250/300-240-2. A multi-parameter analysis was performed to select a cogeneration plant and for the first time is one of the largest district heating plants of Central and Eastern Europe, incorporating several different technologies (gas turbine installation, gas-piston engine). Comprehensive analysis of significant components (technical, economic, environmental, noise, etc. specific) allows making the right investment decision.

Bidirectional Heat Interchange between District Heating and Cooling Plant and Customers with Solar Heat Utilization Systems

Bidirectional Heat Interchange between District Heating and Cooling Plant and Customers with Solar Heat Utilization Systems

Performance Assessment of Using Various Solar Radiation Data in Modelling Large-Scale Solar Thermal Systems Integrated in District Heating Networks

A gap has been identified regarding the impact that using radiation data models have when modelling large-scale solar thermal systems integrated in district heating (DH) systems. Therefore, it is analysed how using satellite-based radiation data models (SARAH), reanalysis models (CFSR, ERA and MERRA2) and other data models (Danish Reference Year) affect the modelling of these systems. Taking three plants in Denmark as study cases, the measured radiation between 2016 and 2019 is compared.Using energyPRO-based mathematical models of the systems, heat outputs are calculated and compared with measured data. Moreover, the yearly DH plant operational cost is calculated to observe the economic impact of using inaccurate models. It is found that heat production assessments based on the SARAH model show a better agreement with measured data than the reanalysis-based ERA5, MERRA2 and CFSR respectively. The empirically-based DRY shows low errors when observing its yearly values but has a higher inaccuracy on the hourly level,providing inaccurate operation profiles of the plant.Additionally, the satellite-based solar data model SARAH is further analysed to identify patterns of its inaccuracy. After comparing it with 18 locations in Denmark using month-hourly profiles, no errors trend can be identified, proving the robustness of the model.

Classification of Measures for Dealing with District Heating Load Variations—A Systematic Review

The highly varying character of district heating (DH) demand results in low capacity utilization of the DH plants, as well as increased use of fossil fuels during peak demand. The aim of this study is to present an overview and a comprehensive classification of measures intended to manage these load variations. A systematic literature review was conducted based on previously defined search strings as well as inclusion and exclusion criteria. Two scientific databases were used as data sources. Based on 96 detected publications, the measures were categorized as (1) complementing DH production in heat-only boilers (HOBs), or geothermal or booster heat pumps (HPs) (usually controlled by the DH company), (2) thermal energy (TE) storage in storage units or in the network (controlled by the company), and (3) demand side measures, which can be strategic demand increase, direct demand response (DR), or indirect DR. While the company has control over direct DR (e.g., thermal storage in the thermal mass of the buildings), indirect DR is based on communication between the customer and the company, where the customer has complete control. The multi-disciplinary nature of this topic requires an interdisciplinary approach.

Logistic characteristics and requirements of Swedish wood biofuel heating plants

The demand for wood biofuel for district heating plants and combined heat and power plants (CHPs) has increased, caused by an increase in both the number and size of CHPs. This places large demands on the logistics system supplying these plants with fuel, with a particular interest in the use of alternative modes of transport such as rail and sea. The aim of this paper is to identify the industry actors’ requirements, constraints, and preferences regarding the wood-biofuel supply chain and to identify the logistical challenges this entails, as well as how this impacts the opportunity for an increased use of alternative transport solutions. A survey was sent to all Swedish CHPs, combined with six interviews with transport companies, terminal operators, and forest companies. The study shows that the industry has a local focus that limits potential logistics and sourcing solutions. It is also challenged by urban sprawl, with expanding residential areas close to the CHPs putting further constraints on the operations. Significant variations in fuel demand, depending on unpredictable outside temperature and seasonal variation, is a further challenge. The low density of the fuel has a negative impact on transport costs and introduces a trade-off between chipping close to the forest to increase density versus more efficient chipping at the CHP. Intermodal transport only used by large plants, driven by a shortage of local fuel.

Recycling of ash from co-incineration of waste wood and forest fuels: An overlooked challenge in a circular bioenergy system

Wood ash recycling to forests after logging residues harvest is important to ensure long-term sustainable forest management, however, it is not recycled in Sweden at the level required to compensate for current logging residue out-take. A problem in this context is wood ash contamination through co-incineration of waste wood with forest fuels, a practice driven by the political goal of a circular bioenergy system. We performed a case study of co-incineration at a typical Swedish district heating (DH) plant, which showed that the forest fuel ash alone could be recycled to forests due to high nutrient levels. Co-incineration with waste wood resulted however in such high levels of contaminants that the ash was landfilled as hazardous waste. Our assessment of the Swedish DH sector showed that wood ash contamination through co-incineration is common, and that only a minor proportion of the ash from forest fuels is recycled to the forest. It also revealed a lack of reliable data regarding ash production and management, making implementation and evaluation of effective countermeasures difficult. Practical measures to enable wood ash recycling, such as removal of waste wood from the fuel mix, incineration of separate fuels, and ash after-treatment, are hampered by technical and economic barriers. Furthermore, no comprehensive policy tools currently exist on either a national or EU level that facilitate wood ash recycling. Thus, we conclude that comprehensive and efficient policy tools are urgently needed to overcome current barriers, and stimulate large-scale recycling of wood ash for long-term sustainable forest fuel utilisation.

Methodology for analyzing operation data for optimum district heating (DH) system design: Ten-year data of Omsk, Russia

The purpose of this paper is to provide an operation-based methodology for optimum district heating (DH) system design. The novelty is (1) analyzing long-term profiles of supply temperature, (2) considering actual DH operational data (3) considering both environmental and technical trends, (4) addressing the problems of detecting operational issues and proposing new design solutions. From the methodological point of view, the assessment methodology, that was originally defined in the statistical terms and which is able to quantify the number of temperature sojourns and quality of system management, have been implemented in the tool. Based on the temperature profiles and charts based on a statistical analysis, the flows and all supply and return temperatures may be forecasted for each actual temperature. The method indicates whether DH plant temperature control is appropriate or not; are any improvements required. The method is also able to show adjustments at the substation valves (secondary side). That means that we can analyze other DH systems and even show are they ready for transition to the 4GDH. To sum up, the main advantage of the developed method is the multiple focus on showing and proofing are any improvements of the network and control logic required.