Gasification Char as a Potential Substitute of Activated Carbon in Adsorption Applications

Abstract This study points out the similarities between char from biomass gasification and activated carbon and reviews its successful applications in the field of adsorption. Surface area (S BET ) is considered as the standard parameter. Since only few data on biomass gasification char are available in the literature, in this work char residues from different commercial gasification plants were collected and characterized, reporting their S BET values for comparison. The highest values for S BET are associated to dual-stage gasification technologies and are highly affected by the operating temperature

Experimental and Modelling Analysis of Char Decomposition: Experiences with Real Scale Gasification Systems

Abstract The main issue to be faced when dealing with gasification processes is the removal of tars in order to obtain a good quality producer gas for later use, either as energy vector or for production of chemicals. Char has been observed to have a high potential for catalytic tar reduction, but the properties that promote this activity are still being investigated. An understanding of the mechanisms involved in the process of tar removal is needed, including the deactivation of the char as a catalyst and its degradation. This work addresses the process of thermal decomposition of char with different operating conditions and under inert atmosphere (N 2 ), in order to determine the mass loss occurring under high temperature treatment. For this purpose, chars collected from local gasification plants have been used. Firstly, a complete characterization of the chars has been carried out to determine their composition, heating value and BET surface area. Secondly, thermogravimetric analyses have been used to calibrate a one-step kinetic model for describing the kinetics involved in the process of char thermal decomposition. The coupling of the kinetics with a CFD model allowed then to consider mass, heat, and momentum transfer phenomena, and to quantitatively estimate the decomposition in a fixed-bed test reactor. The model, whose results have been compared to reference experimental tests, predicts satisfactorily the thermal behavior of the char inside the reactor and its mass loss

5th generation district heating and cooling systems: A review of existing cases in Europe

Abstract This article investigates 40 thermal networks in operation in Europe that are able to cover both the heating and cooling demands of buildings by means of distributed heat pumps installed at the customer substations. The technology of thermal networks that work at a temperature close to the ground, can strongly contribute to the decarbonisation of the heating and cooling sector and furthermore exploit a multitude of low temperature heat sources. Nevertheless, the nomenclature used in literature shows that misinterpretations could easily result when comparing the different concepts of thermal networks that operate at a temperature level lower than traditional district heating. The scope of this work is to revise the definitions encountered and to introduce an unambiguous definition of Fifth-Generation District Heating and Cooling networks. A drawback-benefit analysis is presented to identify the pros and cons of such technology. The survey on the current networks shows that on average three Fifth-Generation District Heating and Cooling systems per year have entered the heating and cooling market in the last decade. Pioneer countries in such technology are Germany and Switzerland. For some networks, the assessed Linear Heating Power Demand Density results are lower than the feasibility threshold adopted in traditional district heating. High performances and low non-renewable primary energy factors are achieved in systems that exploit a very high share of renewable or urban excess heat sources. With respect to traditional district heating, the surveyed pumping energy consumptions result one order of magnitude higher, whereas the implemented control strategies can be completely different, leading the network temperature to float freely

Building Simulation Applications BSA 2015 - Proceedings of 2nd IBPSA-Italy conference

Building Simulation Applications 2015 was the second IBPSA-Italy regional conference on building performance simulation, which took place for the second time at the Free University of Bozen/Bolzano from 4 to 6 February 2015. Almost 100 attendees, 198 authors, 67 presentations, and 4 keynote speakers confirmed not only the interest in building simulation, but also the enhancement of the level of detail, the extension of the size and application range of the domain of investigation and the increase in the level of accuracy and generality of the results. In particular, four sections were devoted to the detailed modelling of phenomena and components (advanced modelling, solar radiation, energy systems and envelope modelling), three to the integrated and non-energy performance analysis (lighting and user behavior), three to the optimization techniques for high performance buildings and retrofit, and two to the development and validation of new tools

Complementarity between Combined Heat and Power Systems, Solar PV and Hydropower at a District Level: Sensitivity to Climate Characteristics along an Alpine Transect

Combined heat and power systems (CHP) produce heat and electricity simultaneously. Their resulting high efficiency makes them more attractive from the energy managers’ perspective than other conventional thermal systems. Although heat is a by-product of the electricity generation process, system operators usually operate CHP systems to satisfy heat demand. Electricity generation from CHP is thus driven by the heat demand, which follows the variability of seasonal temperature, and thus is not always correlated with the fluctuation of electricity demand. Consequently, from the perspective of the electricity grid operator, CHP systems can be seen as a non-controllable energy source similar to other renewable energy sources such as solar, wind or hydro. In this study, we investigate how ‘non-controllable’ electricity generation from CHP systems combines with ‘non-controllable’ electricity generation from solar photovoltaic panels (PV) and run-of-the river (RoR) hydropower at a district level. Only these three energy sources are considered within a 100% renewable mix scenario. Energy mixes with different shares of CHP, solar and RoR are evaluated regarding their contribution to total energy supply and their capacity to reduce generation variability. This analysis is carried out over an ensemble of seventeen catchments in North Eastern Italy located along a climate transect ranging from high elevation and snow dominated head-water catchments to rain-fed and wet basins at lower elevations. Results show that at a district scale, integration of CHP systems with solar photovoltaic and RoR hydropower leads to higher demand satisfaction and lower variability of the electricity balance. Results also show that including CHP in the energy mix modifies the optimal relative share between solar and RoR power generation. Results are consistent across the climate transect. For some districts, using the electricity from CHP might also be a better solution than building energy storage for solar PV

Modelling Of The Thermal Behavior Of Walls And Floors In Contact With The Ground

One of the most complex configuration to model in detail, both in the dynamic simulation of buildings and in the analytical quasi steady-state calculations, is the thermal dispersion through the walls and the floor in contact with the ground. The problem consists in determining the boundary conditions of the external wall surface directly exposed to the soil, whose temperature cannot be considered undisturbed. Different studies, both experimental and numerical, have been carried out in the last decades in order to determine the ground boundary conditions, some of which have been used to elaborate the technical standard EN ISO 13370. This standard gives some indications about the conditions to be considered in the use of quasi steady-state methods and within the dynamic simulation. The evaluation of the simulation software in the specific context of the ground heat transmission, has also driven the IEA to define a specific series of validation cases, the BESTEST In-depth ground coupled heat transfer tests. The present research aim is to test implement reliable calculation procedures for the thermal dispersion through the building envelope towards the ground, in dynamic simulation modelling systems. In this work, a test case of the EN ISO 13370 standard has been modelled with FEM codes, both in steady-state conditions and also in periodic external conditions. Different types of floor have been considered, with different thickness and position of the insulation layer. The results have been compared with those calculated following the prescriptions of the standard EN ISO 13370

Simulation Of Efficiency Of Different Configurations Of Residential Hybrid Heating Systems Combining Boiler And Heat Pump

The contribution of residential buildings primary energy consumption in the U.S. accounts for more than 20% of the total. In this context, improving the efficiency of heating systems represents a key point for keeping up with the carbon reduction goals. Air-to-water heat pumps are a promising technology that has been deeply studied in recent years. Their main advantage is to improve the share of renewables. Nevertheless, they have some drawbacks, such as the poor efficiency at low ambient temperatures and at high supply water temperatures, necessary e.g. for domestic hot water production and in high temperature heating systems. The latter can be found in a high percentage of the building stock. Hybrid systems combining heat pumps and boilers (HHPS) can represent a viable solution to overcome these issues. The sizing of the generators and the control logic according to which they are operated play an important role in the performance of the system. For this purpose, comprehensive studies analyzing different types of buildings in different climates and considering both space heating (SH) and domestic hot water (DHW) production are still missing in the literature. The aim of this work is to identify the best configuration of system, in terms of primary energy consumption, for different heating loads. To do so, a model of the hybrid system is firstly developed by means of a technical computing language (TCL) software. It includes the control logic, that manages the switching of the devices according to the operating conditions. The TCL model has been combined with a dynamic building simulation (DBS). Two different configurations of HHPS were analyzed varying different parameters, such as building thermal insulation, type of heating emission system, DHW demand profile and climate, with a corresponding demand of SH and DHW. The hybrid configurations are compared to a heat pump only solution. The paper presents the results of the simulations with the aim of identifying the most efficient system configuration for each set of parameters considered, in terms of primary energy consumption

Common reeds (Phragmites australis) as sustainable energy source: experimental and modelling analysis of torrefaction and pyrolysis processes

The aim of this study is to apply advanced analytical techniques and kinetic modelling to common reeds (Phragmites australis) to characterize its pyrolysis and torrefaction as possible environmental friendly and sustainable pathways of fuel upgrading. Simultaneous thermogravimetric and differential scanning calorimetry analysis have been carried out on common reeds. The evolved gases during the decomposition process have been analysed by a coupled infrared gas analyser and gas chromatograph/mass spectrometer. Different reed origins (China and Italy) and plant parts (stem and leaves) have been compared. The results have been used to calibrate a torrefaction kinetic model. The model has also been tested simulating a reed torrefaction run occurring in a bench-scale apparatus, supplementing the chemical analysis with a thermal simulation of the reactor carried out through a finite elements approach. The results show that the proposed modelling approach allows the prediction of the reaction products with a satisfying degree of accuracy. Besides its phytodepuration potential, P. australis has proven to be an interesting natural biomass resource for thermochemical conversion processes and energy production both for its suitability and availability

Enhanced Performance Buildings Connected to District Heating Systems: Multi-Objective Optimisation Analysis

The European directive 2010/31/EU states that within the end of 2020, all new buildings should be nearly zero-energy buildings (NZEB), and in the meanwhile, new and renovated buildings performance should comply with new requisites established through a cost-optimal approach. For new buildings, Member States shall ensure that, before construction starts, the technical, environmental and economic feasibility of high-efficiency alternative systems are considered and taken into account, such as, among others, decentralised energy supply systems based on energy from renewable sources, cogeneration, district or block heating or cooling. However, the reduction of the heat needs of the buildings causes a partial utilization of the district heating (DH) capacity with a consequent possible reduction of the distribution efficiency. How to combine the reduction of energy needs and their duration with the technical and economical sustainability of DH and cogeneration systems is an open question. This paper aims to define the cost-optimal solutions of refurbishment for buildings connected to a DH considering the impact on both the heat demand reduction and network distribution losses. The possibility to shift to a low-temperature DH is considered a feasible solution to reduce thermal losses and hence increasing the network efficiency that is connected with a systematic approach to the refurbishment of the connected buildings. For this purpose, an integrated model has been developed and calibrated on real data of a DH system based on biomass and located in northern Italy. The energy performance of the coupled DH - buildings system has been assessed taking into account different measures for the improvement of the existing buildings and different numbers of refurbished buildings. The improvements involve building envelope, heating system and strategies of heating management. A multi-objective optimization has been carried out considering the minimization of the energy needs, the minimization of the net present value (NPV) for the final user and the maximization of the distribution efficiency of the DH, in terms of distribution temperature. The optimization has been also carried out considering different prices policies for heat sales according to its temperature level to assess how it can promote the efficiency of the DH. The results highlight the optimal measures that allow the minimum NPV of the building refurbishment and the highest efficiency of the considered DH system

Analysis of the Measurements Reliability in Dynamic Test of the Opaque Envelope

The characterization of the thermal behaviour of opaque building components is essential in early design stage to compare different alternatives. The evaluation of the dynamic thermal response to the external solicitation is necessary for an effective design study especially for the climates with important annual cooling demand, such as Southern European ones. According to EN ISO 13786, opaque elements can be characterized through some dynamic parameters (i.e., periodic thermal transmittance, time-shift, decrement factor), which can be calculated starting from the wall materials’ thermal properties. However, when either the material thermo-physical properties are unknown (e.g. in existing buildings) or the assumptions on which the method is based are not met (e.g. in platform-frame structures), the calculation method does not assure enough accuracy of results. Hence, for these components, a direct measure of these parameters would be extremely useful. Differently from the procedure to determine the steady-state thermal transmission properties, which is well established, there are no standard rules for the experimental measurement of the dynamic parameters. Nevertheless, as demonstrated by some recent works in the literature, it is possible to estimate EN ISO 13786 dynamic parameters from non-destructive measurements based on heat flow meters, HFM. Since these experimental procedures are still under development, the extent to which several aspects limit the accuracy and precision of the measurements are not yet cleared. In this framework, this work presents a theoretical and experimental analysis about the achievable reliability of the post-processing procedure for the evaluation of the dynamic characteristics of opaque constructions by means of HFM-based measurements in modified hotbox apparatus. Experimental and numerical tests have been performed in order to assess the impact of different sources of uncertainty on the estimation of EN ISO 13786 dynamic parameters. In this regard the main source of errors investigated deal with the sample and the hotbox apparatus, e.g. the boundary effects in heat conduction, the edge guarding of the HFM, the noise of eddy close to HFM surface, the stability in time and space of the surface temperature of the sample and the HFM assembly modality. Moreover, several aspects of the HFM are also investigated, such as the HFM calibration curve, the effect of HFM emissivity and the response time constant. A multi-layer timber wall construction has been tested in a modified hotbox apparatus with different boundary conditions, regarding, in particular, temperatures and convective heat transfer mechanisms imposed at the two sides of the specimen. A numerical model of specimen and apparatus has been also developed and calibrated against the experimental data. With this model, we have investigated further conditions related to the material properties and dynamic forcing solicitation, including the noise affecting the thermal field because of the HFM itself. The relative impacts of the different error sources have been quantified, in order to assess future applicability of HFM dynamic approach for in-situ measurements