*Solar Energy in Industrial Processes DOI: http://dx.doi.org/10.5772/intechopen.97008*

demand profile, seasonal heat demand profile [6], temperature intervals,

*Solar Cells - Theory, Materials and Recent Advances*

prohibitions to produce and distribute renewable heat [10], among other.

fraction increases markedly compared to a process without storage [5].

processes, whether they operate continuously or in batches.

integration of solar thermal energy.

**456**

**2. Methodology for the integration of solar thermal energy**

The integration of solar thermal energy must be economically attractive to compete with fossil fuels and it must be flexible in such a way that it can be applied to various real scenarios where there are spatial, economic, operational, and environmental limitations, limiting the amount of solar energy that can be supplied and with it the solar fraction. The irradiance levels of the site constitute a variable that can limit the maximum output temperatures that a network of solar collectors can reach in a period to guarantee the temperature level and the supply of the total or partial thermal load. Any of the previously stated limitations can define the

Whatever the application, the integration of solar thermal energy must be costeffective and environmentally friendly by reducing the generation of greenhouse gases. Although any reduction in the generation of greenhouse gases is an important point for any industrial sector, the design objective should always be the total elimination of the use of fossil fuels. However, the limitations to achieve a solar fraction of unity are real and it is important to evaluate how they can define the installation of the solar thermal device. Each of the restrictions raised is a challenge that must be addressed and resolved to respond to the real needs that arise in the

With the technologies that currently exist for the use of solar energy for heat production, the processes that demand low-temperature heat are the most convenient for integrating solar heat [11], besides, when solar storage is introduced, solar

The evaluation of some of the restrictions or limitations such as: available installation space for the collector network, availability of capital or the low prices of the fossil fuels used and the supply time of the collector network, allows to evaluate the real impact of each scenario when compared with the one where there are no restrictions for the installation of the solar thermal device and thus seek the profitability of the device in whatever the scenario. Next, the proposed methodology for the integration of solar thermal energy with some real restrictions is described. The objective of this chapter is to make a general approach that includes some real scenarios that arise when solar thermal energy is integrated into industrial

continuous, semicontinuous or batch processes, different kinds of solar heat (steam, drying, hot water) [7]; b) regarding to the facilities: location [5], surface area availability; c) depending on the expected objectives: solar fraction, outlet temperatures, payback time, lower emissions of greenhouse gases (GHG), saving costs [8]. However, the picture is not complete if the limitations or restrictions that represent serious challenges to overcome to achieve efficient use of solar energy are not given equal importance: a) inherent to the process: higher process heat demand than solar heat produced; b) regarding to the facilities: limited flexibility of the systems, use of outdated or non-optimal technology for process conditions, higher costs of solar heating systems than fossil fuel conventional systems [6]. And all these considerations must in turn take into account energy policy and the associated investment, which can also limit or restrict the optimal use of solar energy: lack of economic support to research and innovation to tuning and updating of technology, lack of standard procedures for the implementation and evaluation of technological systems, difficulty promoting attractive investment and business models for the deployment and integration of renewable energies, and few market incentives [9],

industrial sector when the transition towards the use of renewable energies is sought to replace fossil fuels.

The methodology developed is general and can be used or coupled to medium temperature solar collectors or mixed systems (low and medium temperature solar collector technologies) for a specific application. The range of applications can be expanded by defining some other objectives of industrial interest.

The approach contemplates the integration of solar thermal energy into a real case, using low-temperature solar collectors, specifically, flat plate solar collectors, for the selection, design, and operation of the collector network. On the other hand, the design of the collector network is based on the most critical conditions of the year, which correspond to the winter period and guarantee the supply of the thermal load throughout the year. It is important to mention that the rest of the year there will be surplus energy that can be used in other applications. In the selected case study, two scenarios will be evaluated. In the first scenario, the total supply of the thermal load is considered at the temperature level required by the process, with a solar fraction of one and zero greenhouse gas emissions to the environment. In this scenario there are no space limitations for the installation of the solar collector network. In the second scenario, it is proposed that only 50% of the area required for the total supply of the thermal load is available, reducing the fraction as the generation of greenhouse gases. In this last scenario, it is analysed how the restrictions impact and what implications it has with the rest of the variables such as:

**Figure 1.**

*Main stages that require thermal energy in an industrial process (green colour): Continuous process (a), batch process (b).*

reduction in emissions, time in the recovery of investment (payback time) and time of direct supply of the collector network.

To carry out the integration of solar thermal energy, it is important to quantify the available solar resource to determine the maximum outlet temperature of the solar collector network, determining the supply time at target temperature and the size of the network. For a batch process, it would be sought that the direct supply time from the network is equal to the time required by the process, otherwise it is necessary to match the availability of the solar resource with the energy requirement of the process at the temperature required by it.

In **Figure 1**, reference is made to the energy requirements of an industrial process and to solar availability, to match these requirements and to be able to integrate solar thermal energy. For the solar energy supply or production curve, it is considered that there is an available area of 1000 m<sup>2</sup> . Section a) represents a continuous process and the energy demand of the process is above the amount that is captured with the available surface (1000 m<sup>2</sup> ), to supply the thermal load, the capture area would be increased. In part b) a batch process is shown where it is observed that the energy requirement can be provided entirely by solar energy.

In this approach it is possible to supply the thermal energy of the process through solar thermal energy using a thermal storage system to match the demand and energy production. The temperature level required for each process operation is not considered in the diagram.

**Figure 2** displays the temperature level required by the process and the temperature provided by the solar collector network. It is observed that during a period of 5 h 45 min (9:45 h - 15:30 h) the target temperature of the process is reached. In the time that the requirement does not coincide with the solar availability, the thermal load would be supplied with the use of storage.

In parallel, the Pinch Analysis methodology can be used, and the energy requirement of the process can be reduced by favouring the process-process heat exchange. These objectives were raised and solved in the work published by Fuentes-Silva et al. [8]. On the other hand, *ΔTmin* is a function of auxiliary services, when increasing the heat recovery area, it is reduced, however, the area of the collector network increases, so it is interesting to evaluate the costs associated with this relationship.

**Figure 3** presents the logic of the proposed methodology for the integration of solar thermal energy into industrial processes, it is represented by a block diagram. The proposed methodology is carried out in some stages simultaneously and feedback is provided until the best conditions for the final design are reached.

**Figure 3.**

**Figure 4.**

**459**

*Flow diagram of dairy process.*

*Design algorithm to integrate solar thermal energy.*

*Solar Energy in Industrial Processes*

*DOI: http://dx.doi.org/10.5772/intechopen.97008*

### **Figure 2.**

*Temperature level required by the process (85 °C) and that supplied by the solar collector network (variable).*

reduction in emissions, time in the recovery of investment (payback time) and time

To carry out the integration of solar thermal energy, it is important to quantify the available solar resource to determine the maximum outlet temperature of the solar collector network, determining the supply time at target temperature and the size of the network. For a batch process, it would be sought that the direct supply time from the network is equal to the time required by the process, otherwise it is necessary to match the availability of the solar resource with the energy require-

In **Figure 1**, reference is made to the energy requirements of an industrial process and to solar availability, to match these requirements and to be able to integrate solar thermal energy. For the solar energy supply or production curve, it is

continuous process and the energy demand of the process is above the amount that

**Figure 2** displays the temperature level required by the process and the temperature provided by the solar collector network. It is observed that during a period of 5 h 45 min (9:45 h - 15:30 h) the target temperature of the process is reached. In the time that the requirement does not coincide with the solar availability, the thermal

capture area would be increased. In part b) a batch process is shown where it is observed that the energy requirement can be provided entirely by solar energy. In this approach it is possible to supply the thermal energy of the process through solar thermal energy using a thermal storage system to match the demand and energy production. The temperature level required for each process operation is

In parallel, the Pinch Analysis methodology can be used, and the energy requirement of the process can be reduced by favouring the process-process heat exchange. These objectives were raised and solved in the work published by

Fuentes-Silva et al. [8]. On the other hand, *ΔTmin* is a function of auxiliary services, when increasing the heat recovery area, it is reduced, however, the area of the collector network increases, so it is interesting to evaluate the costs associated with

**Figure 3** presents the logic of the proposed methodology for the integration of solar thermal energy into industrial processes, it is represented by a block diagram. The proposed methodology is carried out in some stages simultaneously and feed-

*Temperature level required by the process (85 °C) and that supplied by the solar collector network (variable).*

back is provided until the best conditions for the final design are reached.

. Section a) represents a

), to supply the thermal load, the

of direct supply of the collector network.

*Solar Cells - Theory, Materials and Recent Advances*

ment of the process at the temperature required by it.

considered that there is an available area of 1000 m<sup>2</sup>

is captured with the available surface (1000 m<sup>2</sup>

load would be supplied with the use of storage.

not considered in the diagram.

this relationship.

**Figure 2.**

**458**

#### **Figure 3.**

*Design algorithm to integrate solar thermal energy.*

**Figure 4.** *Flow diagram of dairy process.*

### **2.1 Case study**

The case study is a dairy process described in the literature [12]. It operates on batch and the required heat utility is from 8:00 h to 13:00 h (five hours), enough to carry out pasteurisation of milk at 85 °C. Hot water is needful to curd the milk from 8:30 h to 13:00 h (4.5 hours) at 40 °C; more hot water is required at 62 °C to clean the equipment during a period of 2 hours (16:00 h – 18:00 h). **Figure 4** represents the diverse production stages in a dairy plant at required temperatures.

In **Figure 5** the periods of demand for thermal energy of the main operations of the process are shown (squares) and the period of solar energy production is also displayed (parabolic line). **Figure 5** shows the pairing periods, and this allows to determine if the heat supply is direct from the solar collector network or if requires storage, it also helps to define the possible heat exchanges between the process streams to recover energy.

#### **2.2 Energy integration of the process**

Next, Pinch Analysis is used to carry out the integration of solar thermal energy and determine the optimal *ΔTmin*.

Dairy process stream data is shown in **Table 1** including inlet and outlet temperatures and heat capacity. From the data of the currents, the Composite Curves are constructed and determine the minimum hot and cold utilities, and thus the process-process heat exchanges. To deliver the thermal load required by the process, a boiler that produces hot water at 95 °C for 5 hours is used, providing a thermal load of 4,401.01 kWh. The heat transfer coefficients used are 0.8 kW/m2 °C for water and slightly viscous substances and 0.3 kW/m<sup>2</sup> °C for viscous substances.

The Composite Curves provide a scheme of pure countercurrent heat transfer of the process streams for a chosen *ΔTmin*. They are used to determine the minimum heating and cooling requirements of the process and this allows the calculation of the minimum transfer area prior to the detailed design of the heat transfer network.

In **Figure 6** we have the Composite Curves for a *ΔTmin* of 10 °C where the minimum utilities are determined, which are 294.78 and 260.68 kW of heating and cooling, respectively. It is observed that the thermal load and the temperature level of the hot utility can be supplied by solar thermal energy.

Determination of the minimum area assumes that there is vertical heat exchange between the Composite Curves throughout the entire enthalpy range. In the graph of the Composite Curves, we can read the amount of heat that will be transferred

between the streams, as well as the values of the outlet and inlet temperatures (at that interval) of the hot streams, like so the values of the outlet temperatures and entry of cold currents. So if the curves, both for hot and cold currents, correspond to only one of them, as happens between an exchange of process current - auxiliary service, we can estimate the necessary area of heat exchange given by Eq. (1) known as the Bath equation, which is based on the countercurrent heat exchange assumption implicit in the compound curves and this leads to the minimum area, only if the global heat transfer coefficients are equal for all exchanges [13].

**Description Tinlet (°C) Toutlet (°C) CP (kW/°C)** Mains water 12.20 38.00 2.64 Milk- rennets vats 34.00 35.00 3.89 Pasteurised milk- effluent 75.00 44.00 4.38 Water for boiler 95.00 78.00 10.63 Raw milk- input 4.00 35.00 4.38 Milk- input 35.00 75.00 4.38 Mains water- for cooler 12.20 18.00 6.35 Input milk 44.00 36.00 5.84 Water – of storage tank 73.30 40.00 1.94 Water – rennets vats 40.00 38.00 3.89 Water – of storage tank 62.40 25.00 9.30 Water – of storage tank, surplus 62.40 25.00 12.90 Main water -for boiler 12.20 95.00 10.63

> 1 Δ*TML*

The estimate of the total *AHRN* area is obtained by adding the area of each

in the Composite Curves (kW). *hi* and *h*j are the individual transfer coefficients

*hot i* X*: i*

), *qi* and *qj* are the thermal exchange loads obtained from the enthalpies

*qi hi* þ

!

*cold j* X *j*

*q j h j*

(1)

*AHRN* ¼

(kW/m<sup>2</sup> °C). The subscripts *k*, *i* and *j*.

interval (m<sup>2</sup>

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**Table 1.**

**Figure 6.**

*Stream data for dairy process*

*Solar Energy in Industrial Processes*

*DOI: http://dx.doi.org/10.5772/intechopen.97008*

*Composite curves for a ΔTmin of 10 °C.*

*k intervals* X *k*

**Figure 5.** *Pairing between major process operations and available irradiance in a day.*
