Elsevier

Energy

Volume 176, 1 June 2019, Pages 961-979
Energy

Performance analysis of a biomass gasification-based CCHP system integrated with variable-effect LiBr-H2O absorption cooling and desiccant dehumidification

https://doi.org/10.1016/j.energy.2019.04.040Get rights and content

Highlights

  • The variable-effect absorption cooling and desiccant dehumidification were studied.

  • 3E benefits from redwood, woody chips, and sewage sludge schemes were investigated.

  • Total performance is more sensitive to feedstock cost than to natural gas cost.

  • Compared to redwood and sludge, woody chips is the most favorable in Singapore.

Abstract

A novel biomass gasification-based combined cooling, heat and power (CCHP) system, which is composed of a gas-fueled internal combustion engine, variable-effect LiBr-H2O absorption cooling, and dehumidification air-conditioning with desiccant coated heat exchangers, was introduced. The temperature and humidity independent strategy was applied in the gasification-based CCHP system to enhance cooling production, in which the variable-effect absorption chiller and desiccant dehumidification air-conditioning were driven by the exhaust heat and jacket heat of the gas engine based on energy cascade, respectively. The operation strategy of the system followed the electric load. Validated by experimental data, a zero-dimensional code of the gasifier with Gibbs free energy minimization, an artificial neural network model of the variable-effect absorption chiller, and a 1-D dynamic model of the dehumidification air-conditioning, were built with reasonable deviations. The results of energetic, economic, and environmental (3E) analyses for the proposed gasification-based CCHP systems that were applied in two different buildings indicate that woody chips are the most favorable feedstock under the climate of Singapore. The total performance is more sensitive to the feedstock cost than to the natural gas cost. This work enables to contribute valuable data to the practical application of the biomass gasification-based CCHP system in Singapore's building sector.

Introduction

Energy supply and energy security have gained increasing attention throughout the world. It is attributed to that the energy demand is increasing year-by-year while the limited fossil fuel source is decreasing. Continuously exploring sustainable and clean energy sources and technologies has become a key driver to a great number of researchers in this sector, in order to find a more environmentally friendly approach to mitigate emissions (e.g. greenhouse gas). Biomass (e.g. biofuel and organic waste [1]) that dominates renewables shared 5.7% of world primary energy supply in 2016 [2]. In megacities like Singapore, organic solid waste e.g., paper/cardboard, horticulture waste, sewage sludge, etc. is annually generated in huge quantities. In 2016, Singapore annually produced around 7,814,200 tons of solid waste, of which 61% was recycled with the rest await disposal. Non-food organic solid waste (e.g. paper/cardboard, horticulture waste, and sewage sludge) occupied 33.5% of total waste that had to be disposed of in Singapore.

Combustion, pyrolysis, and gasification are by far the main pathways of converting biomass to energy carries ‒ heat, power, synthesis gas or liquid fuels, in which thermochemical gasification [3,4] is an environmentally friendly approach of converting biomass feedstock to more diverse fuels e.g. syngas (mainly composed of H2 and CO) and liquid fuels via Fischer-Tropsch synthesis. These gaseous/liquid fuels can be more efficiently used for power generation or combined cooling, heat and power (CCHP) that is an attractive and mature technology of maximizing the overall energy efficiency at the systematic level. Biomass-fueled gasification CCHP systems [5,6] are playing an increasingly significant role in mitigating climate deterioration and in sustainable economics. Based on the upstream products (e.g. heat, gas, and liquid fuels) of biomass-to-energy processes, the prime movers e.g. internal combustion engines (ICEs) and gas turbines further convert the products to power, heat, and cooling.

The gasifier is a key component in the gasification-based CCHP (G-CCHP) systems. During the past decades, the comprehensive gasification processes with carbonaceous feedstock materials have been widely studied in order to improve the gasification efficiency i.e. cold gas efficiency. Nipattummakul et al. [7] conducted an experimental study on syngas that was generated from sewage sludge by using steam gasification, where the effect of the reaction temperature on the gasification efficiency indicated that the reduction temperature over 1073 K was recommended for the steam gasification with sewage sludge. Umeki et al. [8] numerically analyzed the performance of an updraft biomass gasifier with the high-temperature steam agent and investigated the effect of various steam-to-feedstock ratios. Xiao et al. [9] proposed two-stage fluidized bed gasification to conduct the parametric and performance investigation by using the woody chips and pig manure. Contributed by the steam gasifying process, a high H2 content of 60% was obtained. Olgun et al. [10] designed and established a small-scale fixed-bed downdraft gasifier with agricultural and forest solid waste to study the effect of air-to-fuel ratios on the gasification performance.

At the systematic level of the G-CCHP, most of the investigators aimed to assess the overall performance that involves in the energetic, economic and environmental (3E) impacts via the experiment, simulation, and multiple-scale demonstration. Wang et al. [[11], [12], [13]] have carried out modeling and performance analyses regarding optimization of the biomass gasification-based CCHP system, including produced energy supplied to buildings and hybrid utilization with natural gas. Li et al. [14] evaluated the yearly performance of a 20 kW micro-scale biomass gasification-based CCHP system running under U.S. climate. Patuzzi et al. [15] proposed the scale category for biomass gasification CHP systems, i.e. micro-scale systems (<50 kW), small-scale systems (50 kW–1 MW) and large-scale systems (>1 MW). They compared the various small-scale biomass gasification combined heat and power (CHP) systems utilized in Italy, in which the highest electrical efficiency of 25.3% can be reached corresponding to wood chips feedstock. Puig-Arnavat et al. [16] built a thermodynamic model of a biomass gasification system and conducted a comparative study on performances in different system configurations. Huang et al. [17] focused on the performance assessment on a biomass gasification tri-generation system via modeling prediction. In this paper, three different types of feedstock (willow chip, miscanthus, and rice husk) were compared with respect to energetic and economic benefits when the system supplied to energy profiles of selected buildings. The biomass-fueled G-CCHP systems that are integrated with ICEs are summarized in Table 1 covering the nominal power range of 15–1000 kW (from micro-scale to small-scale).

The majority of research in the literature focused on the single-effect or double-effect absorption cooling driven by the exhaust heat of ICEs, and on domestic hot water produced from coolant water. A biomass gasification-based CCHP system operates the off-design mode frequently to match the load evolution that is affected by weather conditions and building features. However, the conventional single-effect or double-effect absorption cooling cycle has significant limitations in off-design operation e.g. the driving temperature restriction. In addition, buildings in tropical cities like Singapore are in high demands for cooling but not for domestic hot water and space heating. Thus, a novel biomass gasification-based CCHP system (G-CCHP) that adopted the temperature and humidity independent concept was introduced, where state-of-the-art technologies of the variable-effect absorption chiller (VEAC) [18] that is capable of smoothly operating between the single- and double-effect cycles, and desiccant dehumidification (DDAC) with desiccant coated heat exchangers (DCHEs) [26] were integrated in order to maximize cooling output. To date, no such a G-CCHP system has been reported. The objective of this paper is to comprehensively assess the systematic performances of the proposed G-CCHP systems with different feedstock materials (i.e., redwood pellets, woody chips, and sewage sludge) for two types of buildings in Singapore (i.e., data center and commercial building), via 3E analyses based on the experiment, simulation and comparative study with the conventional heating, ventilation, and air conditioning (HVAC) – electricity-driven vapor compression refrigeration. Firstly, the system configuration was introduced and the operation strategy was described subsequently. Secondly, the models of the gasifier, ICE, DDAC, and VEAC were developed and validated with the experimental data collected from on-field and lab test. In addition, the 3E evaluation criteria and total performance were defined. Thirdly, based on the gasifier model, the optimal parameters for the gasification process were obtained. The 3E and total performances of the proposed systematic schemes were evaluated. Sensitivity analysis was conducted to find the effect of the key factors on the total performance. Finally, the major findings were summarized.

Section snippets

System configuration

A G-CCHP system (see Fig. 1) that is fed with solid-waste carbonaceous feedstock is integrated with variable-effect LiBr-H2O absorption cooling and desiccant dehumidification air-conditioning that includes desiccant coated heat exchangers. The proposed G-CCHP system is mainly composed of two subsystems ‒ upper stream subsystem (i.e., a producer gas generation subsystem) and downstream subsystem (i.e., a CCHP subsystem), which can simultaneously supply cooling and power to buildings. To be

Autothermal gasifier

A zero-dimensional thermodynamic equilibrium model [28] with Gibbs free energy minimization (that originated from the Aspen Plus V9 Program [29]) was developed and applied in this work to predict the producer gas composition and yield generated from the gasifier. The equilibrium model is able to calculate the gas yield and composition with a maximum conversion efficiency, which is independent of gasifier configurations [30]. Major assumptions are listed below:

  • The feedstock residence time in the

Model validation

As reported in our previous works [14,48], thermodynamic analysis and 3E (energetic, economic and environmental) benefits evaluation of a 20 kW gasification-based CHP system using redwood pellets have been implemented. Fig. 4 illustrates the 20 kW micro-scale G-CCHP system integrated with a DDAC unit. This system has been demonstrated in Singapore local site to convert woody chips to cooling, heat and power. This system implemented desiccant dehumidification without the VEAC unit. All relevant

Conclusions

A biomass gasification-based CCHP system that was integrated with variable-effect LiBr-H2O absorption for sensible cooling and desiccant dehumidification with desiccant coated heat exchangers for latent cooling was proposed and investigated on potential applications in two types of Singapore's buildings (i.e., data center and commercial building). Models of four key components, including the gasifier, internal combustion engine, desiccant dehumidification air-conditioning, and variable-effect

Acknowledgement

This research is supported by the National Research Foundation (NRF), Prime Minister's Office, Singapore under its Campus for Research Excellence and Technological Enterprise (CREATE) programme (Grant Number R-706-001-101-281). We thank Dr. Zhenyuan Xu from Shanghai Jiao Tong University for the discussion of modeling the variable-effect absorption chiller. Thanks are extended to Dr. Alexander Lin for his kind help on improving the quality of this article.

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