Chinnadurai Karunanithy and Kasiviswanathan Muthukumarappan

Agricultural and Biosystems Engineering, South Dakota State South Dakota

USA

1. Introduction

Renewable energy is gaining importance in satisfying environmental concerns and addressing economical concerns over fossil fuel usage. Lignocellulosic materials are the most abundant renewable resources on earth (Lynd et al., 2005). Energy can be obtained from biomass either biochemically or thermochemically. In the biochemical process, pretreatment of biomass is a necessary and the first step in opening up structure of the biomass cell wall to permit the access of enzymes to cellulose and hemicellulose. Pyrolysis, gasification, and combustion are the three main thermochemical processes to get energy from biomass. Combustion has a maximum efficiency of more than 30% (Yu et al., 2007). Because gasification offers higher efficiency compared to combustion, it has attracted a high level of interest (Bridgwater, 2004). According to Wornat et al (1994), the burning of bio-oils produced through the pyrolysis of biomass is more efficient. Bio-oil also offers advantages in storage and transport and in its versatility as an energy carrier and as a source of chemicals (Bridgwater, 2004).

The thermochemical process can convert a low-carbohydrate or non-fermentable biomass to alcohol fuels, thus adding technological robustness to efforts to achieve the 30 x 30 goal. Pyrolysis is an endothermic reaction wherein thermal decomposition occurs in the absence of oxygen. It is always the first step in gasification and combustion, wherein partial or total oxidation of the substrate occurs. Gas is the main product (85%) in gasification, whereas bio­oil (70-80%) is the main product in most types of pyrolysis. The yield of pyrolysis products such as syngas/ producer gas (mixture of CO and H2), bio-oil, and bio-char (charcoal) would vary depending upon the pyrolysis methods (conventional, fast, vacuum, flash, and ultra), biomass characteristics (feedstock type, moisture content, particle size), and reaction parameters (rate of heating, temperature, and residence time). Bridgwater (2003) listed four essential features to get bio-oil from fast pyrolysis: very high heating rates (1000°C/s), high heat transfer rates (600-1000 W/ cm2), short vapor residence times (typically <2 s), and rapid cooling of pyrolysis vapors and aerosols. Because the heart of a fast pyrolysis process is the reactor, during the last two decades several different reactor designs to meet the rapid heat — transfer requirements have been explored. Achieving very high heating and heat transfer rates during pyrolysis usually require a finely ground biomass feed.

Pyrolysis using microwave irradiation is one of the many ways of converting biomass into high value products and chemicals. Not only does microwave assisted pyrolysis (MAP) not require a high degree of grinding (e. g., large chunk of wood logs can be used) as required in

other fast pyrolysis, it also can handle mixed feedstocks (e. g., municipal solid wastes). Fast internal heating by microwave irradiation has an advantage over conventional heating. Moreover, microwave energy deposition in the dielectric loss mode of heating can cause spatially uniform heating (Miura et al., 2000) and is easy to control. The other technical advantages of MAP over conventional pyrolysis include the lack of necessity of size reduction (powder form) and the absence of need for agitation and fluidization; thus the resulting pyrolytic gas and bio-oils that are cleaner than those from gasification and conventional pyrolysis. The absence of a carrier gas for fluidization results in a higher heating value of the syngas produced. Because microwave heating is a mature technology, developing a microwave heating system for biomass pyrolysis would have a low cost.

Both Bioenergy (International Energy Agency) studies and work performed in Finland have estimated bio-oil to be the lowest-cost liquid biomass-based fuel. The targeted final application would dictate the desirable quality of bio-oils. For example, the calorific value, viscosity, density, surface tension, and distillation characteristics are of critical importance for fuel applications (Garcia-Perez et al., 2006a). The above characteristics can be achieved if bio-oil has (i) a low solid content, (ii) good homogeneity and stability, and (iii) a reasonably high flash point. Solantausta et al (1994) concluded that the use of bio-oil in gas turbines can be increased by optimizing their physical and chemical properties (ash content, alkali content, heating value, and viscosity). The viscosity of bio-oil affects the spray pattern and droplet size. A high viscosity of bio-oil results in high line pressure drops, thereby requiring the fuel pump to work harder in order to maintain a constant flow rate. Doll et al (2008) derived an equation describing automation characteristics of the fuel consisting of terms like characteristic number (K), density (p), Weber number (We), Reynolds number (Re), surface tension (y), and kinematic viscosity (h). In order to get the desired low characteristic number (K), two physical parameters of the fuel that must be governed are the kinematic viscosity (h) and surface tension (y). Moreover, viscosity is considered as the more important of these two factors. The viscosity of bio-oils can vary over a wide range (35-1000 cP at 40 °C) depending on the feedstock and process conditions (Bridgwater, 2004; Czernik & Bridgwater, 2004). According to Diebold (2002), an efficient collection of volatile components during bio-oil production results in a bio-oil with more low-molecular weight components with lower viscosity, better solvency properties, and possibly better storage properties.

In general, the production of bio-oil through pyrolysis is a thermodynamically non­equilibrium process. This process requires only a short residence time in a high temperature zone followed by rapid thermal quenching to produce a bio-oil that is also not at equilibrium (Ringer et al., 2006). The presences of many reactive organic compounds in the bio-oil interact to achieve equilibrium during storage. The reactions result in the formation of larger molecules and consequently increase the viscosity of the bio-oil (Diebold & Czernik, 1997; Ringer et al., 2006). Because of the high oxygen (40-50 wt %) and water content (15-30 wt %) and the low H/C ratios, bio-oils cannot be used as transportation fuels directly without prior upgrading. As mentioned earlier additional obstacles are the limited stability of the bio-oils under storage conditions due to the presence of unsaturated compounds and their minor miscibility with conventional liquid fuels (Samolada et al., 2000). Catalytic biomass pyrolysis is a promising approach due to the elimination of costly condensation and re-evaporation procedures prior to bio-oil upgrading (Samolada et al., 2000; Lu et al., 2009a).

Several studies have indicated that the viscosity of bio-oil depends on the type of feedstocks, type of pyrolyzer, and pyrolysis conditions. The type of feedstock is the main variable that affects the quality of the bio-oil apart from the postproduction processing techniques. In order to gain a better understanding of the effect of feedstock on product quality, a comparison of feedstocks is needed (Oasmaa et al., 2005a). Accordingly, the current study was undertaken to compare the viscosity of bio-oils produced from different feedstocks through microwave pyrolysis and to characterize them using storage and loss moduli.

Venderbosch R. H.1 and Heeres H. J.2 1BTG Biomass Technology Group B. V. 2RijksUniversiteit Groningen The Netherlands

1. Introduction

Being the only sustainable product containing carbon, biomass is the only alternative for fossil derived crude oil derivatives. Research on the use of biomass for first generation biofuels is rapidly expanding (e. g. bio-ethanol from sugar sources and starches and bio­diesel from pure plant oils). Biomass, and in a particular ligno-cellulosic material, is difficult to convert easily into transportation fuels. Research is focused on indirect routes like: i) the fractionation of biomass and fermentation of the cellulosic and hemi-cellulosic fraction to ethanol, and ii) the destructive gasification of the complete biomass to produce syngas for further upgrading to e. g. methanol or Fischer-Tropsch diesel. Conventional refinery scales (up to 100 t/hr crude oil equivalence) are preferred for economic reason, but problematic for biomass resources, as biomass is scattered and collection is costly. In addition, various types of biomass are very different in structure and composition, have a low energy density compared to many fossil resources, and often contain significant amounts of water and ash. Such disadvantages can be overcome if the biomass is first de-centrally restructured, densified at a scale of 2 to 10 t/hr, and (preferably simultaneously) ‘decontaminated’. The intermediate product is then transported to a large central processing unit where it is transformed to the final product (at a scale of say 50 to 200 t/hr). A potentially attractive technology for this purpose is fast pyrolysis (see recent review of Venderbosch&Prins, 2010). Pyrolysis liquids contain negligible amounts of ash, and have a volumetric energetic density 5 to 20 times higher than the original biomass. However, the oil is acidic in nature, polar and not miscible with conventional crude oil. In addition, it is unstable, as some (re)polymerisation of organic matter in the oil causes an increase in viscosity in time. Pyrolysis oil should thus not be regarded as an oil in a historic perspective, but merely as a carbohydrate rich syrup. Proof for this statement is given by a solvent fractionation method, where the largest part of the oil, up to 70%, can be easily extracted by water. A typical example is presented in Figure 1 (and analysis in Table 1), where pyrolysis oil is divided into several groups of compounds, differing in oxygen functionality and molecular size (Oasmaa et al. 2003; Oasmaa, 2003). Interestingly, the large ether insoluble fraction contains significant amounts of sugar-like components, and has the appearance of a syrup-like liquid. The high levels of oxygen in the pyrolysis oil are reported to be the main cause for the unstable character. However, it may be apparent that not the oxygen itself renders the pyrolysis oil unstable, but the nature/reactivity of the oxygen containing functional chemical groups. Especially the carbonyl compounds (aldehydes, ketones) seem to be

responsible for the thermal instability and transformation into less reactive organic groups (f. i. to the corresponding alcohols) seems a viable option.

Table 1. Chemical composition of reference pine oil and its fractions (Oasmaa, 2003)

A number of catalytic approaches have been proposed to upgrade and improve the product properties of fast pyrolysis oil. A well known example is catalytic cracking of pure biomass and/or pyrolysis oil to oxygen-free products. However, this approach is accompanied by a significant amount of coke production (up to 40 wt.% of the biomass) (Horne &Williams, 1996; Vispute et al., 2010) and this issue needs to be resolved.

A number of studies have been performed with the objective to remove the bound oxygen in the form of CO and/or CO2 by decarbonylation and decarboxylation reactions, either thermally or catalytically. The thermal process is known as the HPTT process, a high pressure temperature treatment (De Miguel Mercader et al., 2010). However, oxygen removal beyond a level of 10% appears very difficult with this approach, even when using catalysts, and the product is highly viscous, limiting its application potential.

Catalytic hydroprocessing or hydrotreating of fast pyrolysis oil is a more promising option (Conti, 1997; Elliott, 2007; Elliott et al.; 2009; Kaiser 1997; Rep et al., 2006). In this process, the fast-pyrolysis oil is treated with hydrogen in the presence of a heterogeneous catalyst with the aim to hydro(deoxy)genate the pyrolysis oil to a product with improved product properties.

A potentially attractive outlet for the upgraded oils is its use as co-feed in existing oil refinery units. This enables partial substitution of the fossil carbon in liquid transportation fuels by renewable carbon from biomass in existing infrastructure as proposed in the European Biocoup project. As such, it is expected to lower the investment costs and to facilitate other barriers for introduction of the fast pyrolysis technology. Crude pyrolysis oil, however, cannot be used for co-feeding purposes. It is immiscible with typical petroleum feeds (such as vacuum gas oil) due to the presence of polar components, but moreover, it is highly acidic due to the presence of organic acids (up to 10 wt%) (Oasmaa, 2003) leading to corrosion issues and possibly detrimental effects on typical catalysts in the refinery units (e. g. zeolites in the FCC process) (Dimitrijevic et al., 2006). Furthermore, it has a strong tendency for coking at elevated temperatures.

An alternative product outlet for upgraded pyrolysis oils is the direct use as a green transportation fuel in internal combustion engines. This will require deep hydrotreatment of the pyrolysis oil to an upgraded oil with very low oxygen levels (preferably below 1%) in order to mimic the product properties of conventional hydrocarbon fuels. Hydrogen consumption is expected to be high for this case, and will have a negative impact on the process economics.

This chapter on catalytic hydrotreatment of fast pyrolysis oil is divided in a number of subtopics. A short overview of typical catalysts for the hydrotreatment of pyrolysis oils will be given in part 2, followed by an overview of typical process requirements. Subsequently, in depth process studies using Ru/ C as catalyst for the upgrading of fast pyrolysis oil will be provided (part 3). The effect of process conditions on yields, hydrogen uptake and relevant product properties will be discussed and rationalized by a reaction network. On the basis of these findings, improved catalyst formulations have been designed and their performance will be discussed and evaluated (part 5).

The density of pellet is calculated from the mass and volume (measuring the length and diameter) of compacts. In general, the density of pellets from agricultural straw significantly increases with an increase in applied pressure at any specific hammer mill screen size. An increase in pressure results in plastic deformation of ground particles and consequently leads to pellets that have densities closer to their respective particle densities (Adapa et al., 2010a; Kaliyan and Morey, 2009; Mani et al., 2004). The Application of pre-treatment has been observed to significantly increase the pellet density since pre-treated straw has lower geometric particle diameters and significantly higher particle densities (Adapa et al., 2010a; Kashaninejad and Tabil, 2011). Usually, it has been reported that an increase in moisture content from 10% and up results in a significant decrease in pellet quality (Hill and Pulkinen, 1988; Li and Liu, 2000; Obernberger and Thek, 2004; Shaw and Tabil, 2007). In general, a decrease in hammer mill screen size results in an increase in pellet density (Adapa et al., 2010a; Kaliyan and Morey, 2009; Kashaninejad et al., 2011; Mani et al., 2004). A comprehensive literature on various single-pellet compression test data is provided in Table 2.

Adapa et al. (2010a) reported that the type of agricultural biomass did not have any significant effect on pellet density, while steam explosion pre-treatment, applied pressure and screen size had significant effects. In addition, correlation for pellet density with applied pressure and hammer mill screen size having highest R2 values were developed (Table 3). Similarly, Kaliyan and Morey (2009) indicated that the pellet density of corn stover or switchgrass briquettes was significantly affected by pressure, particle size, moisture content and preheating temperature. Kashaninejad and Tabil (2011) also indicated that the pellets made from microwave-chemical pretreated biomass grinds had a significantly higher
density and tensile strength than the untreated or samples pretreated by microwave — distilled water.

The densities of pellets should also be measured after a storage period of one week to one month to ascertain its dimensional stability, and associated handling and storage costs (Adapa et al., 2010b; Kaliyan and Morey, 2009). Adapa et al. (2010b) reported that a reduction in pellet density is usually expected due to relaxation of grinds in the pellet after release of pressure. They have observed that the relaxation was higher for larger hammer mill screen sizes and lower applied pressures. In some cases, the average reduction in density was negative giving the impression that pellet density actually increased during storage period. However, these negative values are primarily due to higher standard deviations in pellet density measurements. Therefore, from a practical manufacturing point of view, these values should be considered as a zero percent change in pellet density (Adapa et al., 2010b).

31.6 MPa 63.2 MPa 94.7 MPa 138.9 MPa 31.6 MPa 63.2 MPa 94.7 MPa 138.9 MPa

Barley and wheat Hammer Mill Screen Size: 1.6 mm straw Applied Pressure: 126.3 MPa

Moisture Content: 12% (w. b.)

Treatment: Non-Treated (NT),

Microwave Pretreated (MT) and Microwave-Chemical Pretreated (MCT) Wheat — MT 1032 kg/m3

Wheat — MCT 1431

Poplar Wood Hammer Mill Screen Size: 3.2 and 0.8 and Wheat Straw mm

Applied Pressure: 31.6, 63.2, 94.7 and 126.3 MPa

Moisture Content: 9 and 15% (w. b.) Pre-Heat Die Temperature: 70 and 100°C

Treatment: Non-Treated (NT) and Steam Exploded (SE)

Table 2. Comprehensive literature review on single-pellet compression tests for agricultural biomass as feedstock for biofuel

Note: p — Density, kg/m3; NT — Non-Treated; SE — Steam Exploded; P — Pressure, MPa; S — Hammer Mill Screen Size, mm

Table 3. Correlation for pellet density (p, kg/m3) with applied pressure (P, MPa) and hammer mill screen size (S, mm) for non-treated and steam exploded straw grinds.

Apart from an in-depth look at the molecular ultrastructure of different plant cell walls, Scanning Electron Microscopy (SEM) can be utilized to swiftly characterize biomass samples from different pretreatment protocols and while 2D in nature provides a 3D impression of the effect such protocols had on plant cell walls. SEM uses backscattering properties of heavy atom-coated surfaces to determine surface topologies. SEM is strictly a surface technique, and while not yielding information about the inside of an object, it provides fast overviews of large areas at fairly high resolutions with relatively simple sample preparation, allowing rapid screening of many samples. Focused Ion Beam (FIB)/SEM is a promising new method that can provide continuous 3D information over a large depth range though it requires a much more sophisticated sample preparation as compared to conventional SEM and will be discussed further below.

Regarding sample preparation, usually, the best approach is to work with cross sections of plant stems (e. g. Arabidopsis or Brachopodium) that can be cut using a vibrating blade microtome (e. g. Leica VT1000S, Leica Microsystems), resulting in reproducible cross sections. In order to ensure reproducible results multiple sections of each stem are typically cut in water, picked up with a brush or a pair of very fine tweezers and placed on prepared SEM sample stubs. The sample can then be dehydrated and critical-point dried or directly mounted on sample stubs and sputter coated, which allows for better conductivity of the sample and therefore better SEM imaging results.

TEM with plant stem cross sections requires significantly more preparation than SEM (see section above), but yields more quantitative information regarding cell wall thickness and can discriminate between primary and secondary cell wall. We (Li et al. 2009, Qetinkol et al.

2010) have used the described SEM techniques to visualize the effects of different pretreatment techniques designed to break up plant parts before they can be subjected to either enzymes or microbes thus converting them into sugars and subsequently second or third generation biofuels. Both TEM and SEM were used (Yin et al. 2011) to visualize the isolation of plant organelles or changes of the plant structure due to mutations, affecting cell wall properties and susceptibility to deconstruction for second or third generation biofuels synthesis. Furthermore, SEM analysis can be used to study the fracture pattern in samples derived from the mechanical stress screening in order to determine whether the fracture pattern indicate ductile or brittle behavior.

Next, we introduce the examples of process design through BT process. As we mentioned before, there would be many energy paths through BT process. Here, as the examples, H2 production and Cogeneration system (CGS) would be concentrated. The purpose of each process design would be due to the energy analysis and/or the environmental one using LCA methodology.

2.2.1 Case study of Bio-H2 production system

Through a reaction process based on superheated steam, the biomass is converted to the syngas with a high concentration of H2. In the BT process, pyrolysis gases are reformed with H2O (steam), and Tar and Char are generated as co-products. Since Tar contents pass through the higher temperature zone, the residual volume would be negligible. Also, due to the recycling of the sensible heat of syngas, the total efficiency of the entire system would be improved.

Here, the process design of Bio-H2 was executed by the consideration of basic experimental results.

The capability of the biomass gasification plant is 12 t/d, and the annual operation days are 300 day/yr. In the process design, the heat energy generated from the gasifier was assumed to be utilized as the energy for materials dryer. Due to the recycling of thermal energy, the energy of dryer can be reduced at most. For instance, the moisture content can be compensated up to 42 wt.% against the initial moisture content of 50 wt. %. The syngas generated through BT gasifier is transferred to the shift-reaction convertor, and then is fed
into PSA (Pressure Swing Adsorption). In the PSA, the high concentrated H2 gas was purified to 99.99Vol.% (4N) of H2 gas.

Here, Tables 4 shows the performance of Bio-H2 production system. In Tables 4, the cold gas efficiency цСоіл is defined as follows:

Syngas [MJ/h]

^cdd Feedstock [MJ/h] + Char [MJ/h] + Offgas [MJ/h] Also, the total efficiency ^Toid of this system is

_ Bio-H2 [MJ/h]

ЧтоШ Feedstock [MJ/h]

Sugar cane contains approximately 12-17% of total sugars, 90% of which are saccharose and 10% are glucose. Milling can extract approximately 95% of the sugar, leaving behind the solid residue. This cane residue goes by the name of bagasse. Sugar cane is washed in order to undergo a primary "crushing" process before milling. The cane juice obtained undergoes a clarification process in which the pH is balanced and cachaga is obtained, which can be sold as animal feed or as a component in mixtures. Fermentation is usually done with the aid of a yeast, Saccharomyces cerevisiae, which is separated in a continuous phase by centrifugation and reused in the fermenter. The fermentation process differs slightly, depending on whether all the juice is used to obtain bioethanol or whether part of it is drawn off to obtain sugar: in the former case, the juice is heated up to 110°C (to reduce the risk of bacterial contamination), then decanted and fermented; in the latter, the crystals formed by concentration are centrifuged, leaving a viscous syrup called molasses.

The extract leaving the fermenter must then be distilled to extract the hydrated ethanol (an azeotropic solution containing 95.5% v/ v of ethanol and 4.5% v/ v of water), which is dehydrated using molecular sieves or azeotropic distillation (i. e. with cyclohexanone or benzene) to obtain a higher-grade, anhydrous ethanol. In addition to ethanol, there is also an aqueous solution leaving the distillation process, that is called residue.

Molasses obtained from sugar cane are the most important raw material for the purposes of bioethanol production. In recent years, however, there have been rising prices and restrictions on the availability of molasses, which have strongly influenced the production of bioethanol (Quintero et al., 2008). Figure 3 shows the flow chart for bioethanol, energy and sugar production from sugar cane.

Figure 1 shows the concept of our new method of gasification by partial oxidation. This production of biomethanol from carbohydrate (Sakai 2001) has been given the term "C1

chemical transformation technology". In this process, the biomass feedstock must be dried and crushed into powder (ca. 1mm in diameter). When the crushed materials are gasified at 900-1000°C with gasifying agent (steam and oxygen), all carbohydrates are transformed to hydrogen (H2), carbon monoxide (CO), carbon dioxide (CO2) and vapor (H2O). The mixture of gases is readily utilized for generating electricity. The mixture of gases is transformed by thermo-chemical reaction to biomethanol under pressure (40-80 atm) with Cu/Zn-based catalyst, too. That is,

CO + 2H2 ^ CH3OH + Q (Radiation of heat)

CO2 + 3H2 ^ CH3OH + H2O + Q (Radiation of heat)

Since methanol or ethanol and the alkaline catalysts are more soluble in the polar glycerol phase, most will be removed when the glycerol is separated from the biodiesel.

However, the biodiesel typically contains 2-4% methanol after the separation, which may constitute as much as 40% of the excess methanol from the reaction. Most processors will recover this methanol using a vacuum stripping process. Any methanol remaining after this stripping process should be removed by the water washing process. Therefore, the residual alcohol level in the biodiesel should be very low. A specific value for the allowable alcohol level is specified in European biodiesel standards (0.2% in EN 14214), but is not included in the ASTM standard. Tests have shown that as little as 1% methanol in the biodiesel can lower the flashpoint of the biodiesel from 170°C to less than 40°C. Therefore, by including a flashpoint specification of 130°C, the ASTM standard limits the amount of alcohol to a very low level (<0.1%). Residual alcohol left in the biodiesel will generally be too small to negatively impact the fuel’s performance. However, lowering the flashpoint presents a potential safety hazard as the fuel may need to be treated more like gasoline, which also has a low flashpoint, than diesel fuel.

Most of the residual catalyst is removed with the glycerol phase. Like the alcohol, remaining catalyst should be removed during the water washing. Although a value for residual catalyst is not included in the ASTM standard, it will be limited by the specification on sulfated ash. Excessive ash in the fuel can lead to engine deposits and high abrasive wear levels. The European standard EN 14214 places limits on calcium and magnesium as well as the alkali metals sodium and potassium.

Biobutanol is not as aggressive as the bioethanol with regard to the engine construction materials, sealants, and plastics. The fuel with 20% v/ v of biobutanol has similar properties to the hydrocarbons in terms of swelling of polymers (Wolf, 2007).

The oxidation stability of biobutanol-gasoline blends may be compromised by potential impurities from biobutanol production (acetic and butyric acid, acetaldehyde and lower alcohols). The impurities in concentrations of 0.1% v/v in 10% v/v biobutanol-gasoline blends (which corresponds to 1% of impurities in biobutanol) can decrease the fuel oxidation stability by about 15%, therefore the purification with regard to the removal of fermentation by-products is very important step in biobutanol production.

The high boiling point of butanol may negatively influence its evaporation from engine oil after oil contamination caused by frequent cold starts. This phenomenon can occur especially at low ambient temperatures, when the fuel leaks into the engine oil through piston rings. In a normal engine operation biobutanol evaporates after the engine warm up and the motor oil additives are re-solved. However, the solubility of oil additives may be at risk in case of frequent cold starts and short routes in cold winter conditions.

To reduce the energy consumption in a process through heat recovery, heating and cooling functions are generally integrated for heat exchange between feed and effluent to introduce heat circulation. A system in which such integration is adopted is called a self-heat exchange system. To maximize the self-heat exchange load, a heat circulation module for the heating and cooling functions of the process unit has been proposed, as shown in Figure 3 (Kansha et al. 2009).

Figure 3 (a) shows a thermal process for gas streams with heat circulation using self-heat recuperation technology. In this process, the feed stream is heated with a heat exchanger (1^2) from a standard temperature, To, to a set temperature, Tn The effluent stream from the following process is pressurized with a compressor to recuperate the heat of the effluent stream (3^4) and the temperature of the stream exiting the compressor is raised to T1 through adiabatic compression. Stream 4 is cooled with a heat exchanger for self-heat exchange (4^5). The effluent stream is then decompressed with an expander to recover part of the work of the compressor. This leads to perfect internal heat circulation through self­heat recuperation. The effluent stream is finally cooled to T0 with a cooler (6^7). Note that the total heating duty is equal to the internal self-heat exchange load, Qhx, without any external heating load, as shown in Fig. 3 (b).

In the case of ideal adiabatic compression and expansion, the input work provided to the compressor performs a heat pumping role in which the effluent temperature can achieve perfect internal heat circulation without any exergy dissipation. Therefore, self-heat recuperation can dramatically reduce energy consumption.

Figure 3 (c) shows a thermal process for vapor/liquid streams with heat circulation using the self-heat recuperation technology. In this process, the feed stream is heated with a heat exchanger (1^2) from a standard temperature, T0, to a set temperature, Tn. The effluent stream from the subsequent process is pressurized with a compressor (3^4). The latent heat can then be exchanged between feed and effluent streams because the boiling temperature of the effluent stream is raised to Tb’ by compression. Thus, the effluent stream is cooled through the heat exchanger for self-heat exchange (4^5) while recuperating its heat. The effluent stream is then depressurized by a valve (5^6) and finally cooled to T0 with a cooler (6^7). This leads to perfect internal heat circulation by self-heat recuperation, similar to the above gas stream case. Note that the total heating duty is equal to the internal self-heat exchange load, QHX, without any external heating load, as shown in Fig. 3 (d). It can be understood that the vapor and liquid sensible heat of the feed stream can be exchanged with the sensible heat of the corresponding effluent stream and the vaporization heat of the feed stream is exchanged with the condensation heat of the effluent stream. As a result, the energy required by the heat circulation module is reduced to 1/22-1/2 of the original by the self-heat exchange system in gas streams and/or vapor/liquid streams.