2. Enhanced process integration technology

Therefore, together with the concern of energy scarcity and environmental issue, further investigation to discover alternative energy carrier is required not only to complement the fossil energy but also for primary utilization by achieving highly efficient energy systems.

Several parameters need to be accomplished for the future energy carrier, including the simple production method, high energy density, and environmentally benign performance. To this, the hydrogen (H2) has the promising potential as an energy carrier [4]. Under the ambient

or natural gas, which leads to the extensive heat capacity [5]. However, against the potentials as the future energy carrier, H2 has severe characteristics in the extremely low volumetric

transportation and storage methods [6]. Thus, instead of dispatching H2 individually, some pretreatment to bond the H2 into the more convenient form of carrier is very beneficial.

Currently, transportation and storage of H2 are carried out by the various schemes, including liquefaction, compression, chemical and physical storages. An alternative solution for H2 storage with high storage capacity and low-risk level can be approached by employing the liquid organic hydrogen carriers (LOHCs) [7]. Covalently bonding the H2 through the hydrogenation process, the LOHCs have the capability to carry out 5–8 wt% of the H2 content [8]. Due to the characteristics of high reversibility (hydrogenation and dehydrogenation processes) in the moderate temperature, low GHG emissions, simple storage, and comfortable transportation method by using vessel or pipeline, LOHCs own the potential for the application of long-distance and large-scale H2 transportation [9]. Moreover, the infrastructure of LOHCs is relatively compatible with current method of fuel transportation, due to the liquid phase of the

The LOHCs cycle involves hydrogenation and dehydrogenation processes. In this process, the generated H2 is exothermically reacted with the particular compounds in the catalytic hydrogenation [11]. Recently available LOHCs include cyclohexane-benzene, decalin-naphthalene, and toluene-methylcyclohexane (MCH) cycles [8]. In this chapter, toluene (C7H8)–MCH (C7H14) cycle is investigated as the LOHC cycle for the transportation and storage of H2. Both toluene and MCH are low cost, stable compound, and high flexibility of transportation as the liquid phase is very reliable in the wide temperature range, which is favorable for long-distance transport and long-term storage. In addition to this understanding, Chiyoda Corporation, a well-established process engineering company in Japan, has testified the applicability of the

The investigation is emphasized on the effort of integrating the corresponding processes, including the drying, gasification, chemical looping, power generation, and the hydrogenation process to achieve optimum energy circulation based on enhanced process integration (EPI) to obtain the excellent energy efficiency of the total system. EPI is a technology to minimize thoroughly the heat loss of the system by applying the combination of exergy recovery and process integration [13]. With EPI, instead of the optimization of each process individually, the entire energy management of the system is observed to develop a high-efficient integrated

) and boiling temperature (252.9C), which leads to the difficult

), much higher than gasoline

condition, H2 owns high gravimetric energy density (120 MJ kg<sup>1</sup>

LOHCs in the room temperature and standard pressure condition [10].

toluene-MCH cycle in a relatively large-scale facility [12].

plant with minimum waste of energy [14].

energy density (10.8 MJ m<sup>3</sup>

258 Gasification for Low-grade Feedstock

The theory of EPI has been introduced and applied to several raw materials, including algae [16], coal [17, 18], biomass wastes [19, 20], and black liquor [21]. EPI is established from two core technologies such as the process integration and the exergy recovery. The latter relates to the concept to circulate the heat throughout a single process. By applying the EPI, overall exergy loss throughout the integrated system can be reduced as the total energy efficiency of the system is improved.

Figure 1 illustrates the principle of heat circulation employed in the integrated system, including an example of the application of the term of exergy elevation of the process stream. Here, the dotted and solid lines represent the cold and hot streams, respectively.

In contrast to conventional process integration technology, the intensification of the process regarding energy efficiency is carried out in EPI through heat circulation to minimize the exergy losses in each process module before performing the overall process integration. Hence, the energy/heat associated with the process is recovered efficiently by employing heat circulation that promotes exergy recovery.

Figure 1. Basic heat circulation principle: (a) exergy elevation and heat coupling and (b) two examples of this method applied for stream exergy elevation: Compression and heat combination.
