**5. Heat transfer in EMbaffle® technology**

An important feature to design a S&T heat exchanger is the average temperature driving force Δ*Tm* that can be calculated from the general global heat transfer equation:

$$Q = U A \Delta T\_m \tag{1}$$

Where *Q* is the duty or heat transferred per unit time, *U* the overall heat transfer coefficient and *A* the heat transfer surface.

In general, Δ*Tm* is determined by the approach temperatures, fluid properties and fluid arrangement. It can be calculated from the logarithmic mean temperature difference applying a correction factor:

$$
\Delta T\_m = \Delta T\_{lm} F\_t \tag{2}
$$

*Ft* is the correction factor and it depends on the S&T exchanger geometry (number of shell/tube passes and flow orientation), and distortion of the shell and tube fluid temperatures profile (thermal leakage through the longitudinal baffle, close approaches, temperature cross, bypass streams).

*EMbaffle® Heat Transfer Technology Step-Up in CO2 Reduction DOI: http://dx.doi.org/10.5772/intechopen.96253*

The correction factor *Ft* ranges from 0 to 1. Typically, values smaller than 0.8 indicate close temperature approaches and therefore an inadequate design for the given process conditions; the design may be easily improved by increasing the correction factor *Ft* switching to a counter-current type exchanger.

EMbaffle® allows to achieve a 100% counter-current configuration thanks to its pure longitudinal flow, maximizing the correction factor *Ft* to 1 and making the exchanger extremely performing where very tight temperature approaches are specified.

#### **5.1 Heat transfer correlations**

In EMbaffle® technology, the shell-side HTC is calculated using the following correlations for the Nusselt number in case of laminar and turbulent flow respectively:

$$Nu = C\_L Re\_h^{0.6} Pr^{0.4} \left(\frac{\mu\_b}{\mu\_w}\right)^{0.14} \tag{3}$$

$$Nu = C\_T Re\_h^{0.8} Pr^{0.4} \left(\frac{\mu\_b}{\mu\_w}\right)^{0.14} \tag{4}$$

The geometry coefficient functions, *CL* and *CT*, account for the enhancement due to the cross flow at the shell entrance and exit conditions. The Reynolds number is calculated as follows:

$$Re\_h = \frac{\rho V\_S D\_h}{\mu\_b} \tag{5}$$

where *VS* is the shell-side velocity and *Dh* is the characteristic diameter.

The shell-side velocity is calculated with the continuity equation, using the following expression for the shell-side flow area:

$$A\_s = \frac{\pi}{4} \left( D\_s^{\;2} - N\_T D\_o^{\;2} \right) \tag{6}$$

The characteristic diameter is four times the nominal flow area divided by the wetted perimeter:

**Figure 9.** *Measured Nusselt number as a function of Reynolds number.*

**5. Heat transfer in EMbaffle® technology**

*From turbulence to heat transfer – Plot of HTC generated by different grid types [3].*

coefficient and *A* the heat transfer surface.

close approaches, temperature cross, bypass streams).

difference applying a correction factor:

equation:

**330**

**Figure 8.**

**Figure 7.**

An important feature to design a S&T heat exchanger is the average temperature

Where *Q* is the duty or heat transferred per unit time, *U* the overall heat transfer

In general, Δ*Tm* is determined by the approach temperatures, fluid properties and fluid arrangement. It can be calculated from the logarithmic mean temperature

*Ft* is the correction factor and it depends on the S&T exchanger geometry (number of shell/tube passes and flow orientation), and distortion of the shell and tube fluid temperatures profile (thermal leakage through the longitudinal baffle,

*Q* ¼ *UA*Δ*Tm* (1)

Δ*Tm* ¼ Δ*TlmFt* (2)

driving force Δ*Tm* that can be calculated from the general global heat transfer

*CFD analysis of turbulent kinetic energy generated by different grid spans, liquid case [3].*

*Heat Transfer - Design, Experimentation and Applications*

The above factors offer a large range of parameter options to provide the best solution in the light of the design constraints requested by the specific application.

Experimental tests had been conducted by different Institutions in order to validate the general heat transfer correlations and the coefficient *CL* and *CT* for different grid types. In **Figure 9** the measured Nusselt number A as a function of Reynolds Number is represented. The shift in prediction curve follows the change of Reynolds exponential dependence.

### **6. Pressure drops in EMbaffle® technology**

Given the peculiar shape of the grids and the longitudinal flow patterns, EMbaffle® is characterized by reduced hydraulic resistance compared to conventional technologies. Due to this feature, in all cases where limited pressure drops are available EMbaffle® can still achieve low pressure drops for widely used TEMA types like E and F, while conventional segmental designs are forced to switch to "Low pressure drop" TEMA-types (G-, H-, J- or X). This results in a definitely more compact and thermo-hydraulically optimized design.

In EMbaffle® technology, shell-side pressure drop is the sum of the longitudinal flow component and the baffle flow component:

$$
\Delta P = \Delta P\_L + \Delta P\_B \tag{8}
$$

*KB* is the correlation factor accounting for the effect of entrance and exit cross

Experimental measurements have been conducted by different Institutions and

The global measured pressure drops are strongly influenced by the entrance and exit cross flow, especially with short experimental heat exchangers, requiring the

In general, the correlations do not fit properly for very high viscous fluids and for extremely high Reynolds number, while fits with proper margin for low viscos-

In a straight comparison between a conventional S&T heat exchanger and the equivalent EMbaffle® heat exchanger under the same duty, EMbaffle® design often results in significant shell-side lower pressure drops, allowing in several experienced cases to sensibly increase the flow rate without asking for increased

Flow-induced vibrations are determined by the interaction of a cross flow with a

physical body; this produces the shedding of alternating vortices, that transfers mechanical energy to the body. If one of the natural frequencies of the body is matched, such a configuration starts to vibrate. Vibration can be mechanical vibra-

In all gas services and high flow-rate cooling services, prevent vibration is a relevant issue for equipment design. While demand of higher and higher flow-rates to be processed is growing, No-Tubes-In-Window (NTIW) design (i.e. the cut portion of the baffles do not accommodate exchanger tubes) with intermediate supports is often the conventional design solution adopted. The same solution approach can also be adopted when low pressure drops are available at the shell

However, removing tubes from the windows ends up in a larger shell diameter with impact on the capital cost; furthermore, NTIW heat exchangers are usually prone to acoustic vibrations, frequently imposing the adoption of a not desired

tion of the tubes or acoustic resonance of the exchanger shell.

flow, depending on the ratio *AB=AS* and the shell length and diameter ratio.

heat exchangers Manufacturers to validate the above correlations.

ity liquid and gases in Reynolds ordinary range of design (**Figure 10**).

cross check of different experimental data.

*Measured pressure drops as a function of Reynolds number.*

*EMbaffle® Heat Transfer Technology Step-Up in CO2 Reduction*

*DOI: http://dx.doi.org/10.5772/intechopen.96253*

pump or compressor consumption.

side.

**333**

**Figure 10.**

**7. Vibrations in EMbaffle® technology**

The expression for the longitudinal component is:

$$
\Delta P\_L = \frac{2\rho f\_F L\_T V\_S^2}{D\_P} \tag{9}
$$

where *DP* is the characteristic diameter, *f <sup>F</sup>* the Fanning friction factor and *LT* the length of the tubes. The characteristic diameter is calculated as follows:

$$D\_p = \frac{4\left[\frac{\pi}{4}\left(D\_s^2 - N\_T D\_o^2\right)\right]}{\pi D\_o} \tag{10}$$

The friction factor is calculated with the following expression:

$$f\_F = \begin{cases} \frac{16}{Re\_p}, Re\_p < 1189\\ \frac{0.079}{Re\_p}, Re\_p \ge 1189 \end{cases} \tag{11}$$

The baffle pressure drop is calculated using the baffle velocity *VB* and a baffle loss coefficient *KB*:

$$
\Delta P\_B = K\_B N\_B \frac{\rho V\_B^2}{2} \tag{12}
$$

*NB*is the number of the baffles. The baffle velocity is determined using the continuity equation with the following definition of the baffle flow area:

$$A\_B = A\_S - A\_R - A\_{EM} \tag{13}$$

*AR*is the ring area, while *AEM* is the projected area of the EMbaffle grid.

*EMbaffle® Heat Transfer Technology Step-Up in CO2 Reduction DOI: http://dx.doi.org/10.5772/intechopen.96253*

The above factors offer a large range of parameter options to provide the best solution in the light of the design constraints requested by the specific application. Experimental tests had been conducted by different Institutions in order to validate the general heat transfer correlations and the coefficient *CL* and *CT* for different grid types. In **Figure 9** the measured Nusselt number A as a function of Reynolds Number is represented. The shift in prediction curve follows the change

Given the peculiar shape of the grids and the longitudinal flow patterns, EMbaffle® is characterized by reduced hydraulic resistance compared to conventional technologies. Due to this feature, in all cases where limited pressure drops are available EMbaffle® can still achieve low pressure drops for widely used TEMA types like E and F, while conventional segmental designs are forced to switch to "Low pressure drop" TEMA-types (G-, H-, J- or X). This results in a definitely more

In EMbaffle® technology, shell-side pressure drop is the sum of the longitudinal

<sup>Δ</sup>*PL* <sup>¼</sup> <sup>2</sup>*<sup>ρ</sup> <sup>f</sup> <sup>F</sup>LTVS*

where *DP* is the characteristic diameter, *f <sup>F</sup>* the Fanning friction factor and *LT*

the length of the tubes. The characteristic diameter is calculated as follows:

<sup>4</sup> *Ds*

16 *Rep*

The baffle pressure drop is calculated using the baffle velocity *VB* and a baffle

0*:*079 *Rep*

Δ*PB* ¼ *KBNB*

*AR*is the ring area, while *AEM* is the projected area of the EMbaffle grid.

continuity equation with the following definition of the baffle flow area:

*NB*is the number of the baffles. The baffle velocity is determined using the

*Dp* <sup>¼</sup> <sup>4</sup> *<sup>π</sup>*

The friction factor is calculated with the following expression:

8 >>><

>>>:

*f <sup>F</sup>* ¼

loss coefficient *KB*:

**332**

*DP*

<sup>2</sup> � *NTDo* <sup>2</sup> � � � � *πDo*

, *Rep* < 1189

<sup>0</sup>*:*<sup>25</sup> , *Rep* ≥ 1189

*ρVB* 2

<sup>2</sup> (12)

*AB* ¼ *AS* � *AR* � *AEM* (13)

Δ*P* ¼ Δ*PL* þ Δ*PB* (8)

(9)

(10)

(11)

2

of Reynolds exponential dependence.

**6. Pressure drops in EMbaffle® technology**

*Heat Transfer - Design, Experimentation and Applications*

compact and thermo-hydraulically optimized design.

The expression for the longitudinal component is:

flow component and the baffle flow component:

**Figure 10.** *Measured pressure drops as a function of Reynolds number.*

*KB* is the correlation factor accounting for the effect of entrance and exit cross flow, depending on the ratio *AB=AS* and the shell length and diameter ratio.

Experimental measurements have been conducted by different Institutions and heat exchangers Manufacturers to validate the above correlations.

The global measured pressure drops are strongly influenced by the entrance and exit cross flow, especially with short experimental heat exchangers, requiring the cross check of different experimental data.

In general, the correlations do not fit properly for very high viscous fluids and for extremely high Reynolds number, while fits with proper margin for low viscosity liquid and gases in Reynolds ordinary range of design (**Figure 10**).

In a straight comparison between a conventional S&T heat exchanger and the equivalent EMbaffle® heat exchanger under the same duty, EMbaffle® design often results in significant shell-side lower pressure drops, allowing in several experienced cases to sensibly increase the flow rate without asking for increased pump or compressor consumption.

#### **7. Vibrations in EMbaffle® technology**

Flow-induced vibrations are determined by the interaction of a cross flow with a physical body; this produces the shedding of alternating vortices, that transfers mechanical energy to the body. If one of the natural frequencies of the body is matched, such a configuration starts to vibrate. Vibration can be mechanical vibration of the tubes or acoustic resonance of the exchanger shell.

In all gas services and high flow-rate cooling services, prevent vibration is a relevant issue for equipment design. While demand of higher and higher flow-rates to be processed is growing, No-Tubes-In-Window (NTIW) design (i.e. the cut portion of the baffles do not accommodate exchanger tubes) with intermediate supports is often the conventional design solution adopted. The same solution approach can also be adopted when low pressure drops are available at the shell side.

However, removing tubes from the windows ends up in a larger shell diameter with impact on the capital cost; furthermore, NTIW heat exchangers are usually prone to acoustic vibrations, frequently imposing the adoption of a not desired

detuning longitudinal plate to suppress the phenomenon (this is typical for shell side Gas service heat exchangers).

Thanks to the strong bundle consistency and the full confinement of all tubes at any grid, EMbaffle® makes use of the full tube layout ensuring the filling of the complete shell section with consequent reduction of the equipment diameter and/or improved heat exchanger performance, while suppressing the risk of acoustic vibrations due to his longitudinal flow design (**Figure 11**).

The unsupported tubes span of the conventional TEMA heat exchanger is governed by the balance between longitudinal and cross flows, limiting the minimum value that can be reached.

The natural frequency of the tubes depends on the tube diameter and thickness, tube material and unsupported tube span, according to the following formula [4]:

$$f\_N = 0.04944C \left[\frac{E \text{Ig}\_c}{W\_c L^4}\right]^{0.5} \tag{14}$$

Dedicated CFD analysis has been performed to study different annular distributor configurations aimed to optimize the fluid-dynamics through the distributor

*Flow velocity distribution at EMbaffle® annular distributor – Top to bottom increased slot size case [5].*

Several geometries were modeled in order to analyze the flow distribution and the performances of each case. The flow velocity distribution at the inlet nozzle is

recirculation, addressing the flow to concentrate on lateral and bottom sides, trend

Decreased Top to Bottom exchanger slots size, contrary to what it could be expected, seems to address to a better uniform flow speed trend, but the dispersion of the flow rates at the entrance cannot be avoided. The average pressure drops are not significantly impacted by the shape of the cut and this supports the simplest and

Thanks to all above provisions, no relative motion between tube and grid is permitted and, therefore, no wearing nor fretting is observed and reported after

EMbaffle technology was originally conceived to enhance the shell side heat transfer by reducing fouling in heat exchange specific applications in refineries and petrochemical plants. By creating a uniform flow in the bundle, dead zones are omitted. By supporting the tubes using expanded metal grid the boundary layer is continuously interrupted thanks to the local increased velocity. By this approach the balance between fouling disposition and removal results at a lower fouling layer

EMbaffle® technology has then been applied to a variety of processes, where complexity of fouling mechanisms does not allow a predictable behavior. Further to the preliminary experimental results coming from authoritative Bodies, the actual performances in fouling reduction are finding systematic confirmation by the out-

Detailed monitoring of fouling development and study of growing rate had been originally concentrated on crude oil application, where fouling is strongly impacting the thermal and hydraulic performances of the exchangers. The overall heat transfer coefficient over time of a segmental baffle type heat exchanger and the same

comes from a number of units installed and operating for several years.

and reduce the relevant correlated pressure drops (**Figure 12**).

*EMbaffle® Heat Transfer Technology Step-Up in CO2 Reduction*

*DOI: http://dx.doi.org/10.5772/intechopen.96253*

cheapest construction solution of the annular inner shell.

years of continuous operations in potential vibration services.

accentuated by clearance reduction.

**Figure 12.**

**8. Fouling in EMbaffle®**

**335**

than in conventional heat exchangers.

showing a large area of the annular distributor to be interested by flow

In an EMbaffle® exchanger, each tube is fully supported at every grid with a typical span ranging between 200 and 300 mm. This very close tube span significantly increases the natural frequency of the tubes, suppressing the risk of a frequency match and consequent vibration.

EMbaffle® is prone to good performances in condensing and boiling services too, e.g. cross-flow condensers, kettle-type reboilers, etc. where heat transfer coefficient is not substantially depending by the flow rate. Allowing the unrestricted shell-side flow thanks to the open structure, potential vibrations phenomena induced by phase transition are prevented, again allowing for a possible increase of shell side flow rate within the same exchanger constrains.

Concerns may apply to the shell-side fluid entrance region: here the flow suddenly changes from radial to longitudinal direction (vice versa at fluid exit), potentially stressing the tubes, specifically at bundle periphery as no annular space is left. Reducing the grids span in correspondence of the inlet/outlet nozzles, stronger tubes confinement can be configured as required to guarantee no vibrations.

The use of an annular chamber to distribute the flow entrance in homogeneous way through the full bundle circumference, further to provide an impingement protection to the directly exposed tubes, ensures at the same time the development of the longitudinal flow through the complete shell section since the first baffle pass.

**Figure 11.** *EMbaffle® exploiting of the full shell area in comparison to NTIW in gas applications.*

*EMbaffle® Heat Transfer Technology Step-Up in CO2 Reduction DOI: http://dx.doi.org/10.5772/intechopen.96253*

detuning longitudinal plate to suppress the phenomenon (this is typical for shell

The unsupported tubes span of the conventional TEMA heat exchanger is governed by the balance between longitudinal and cross flows, limiting the

*<sup>f</sup> <sup>N</sup>* <sup>¼</sup> <sup>0</sup>*:*04944*<sup>C</sup> EIgc*

In an EMbaffle® exchanger, each tube is fully supported at every grid with a typical span ranging between 200 and 300 mm. This very close tube span significantly increases the natural frequency of the tubes, suppressing the risk of a frequency match

EMbaffle® is prone to good performances in condensing and boiling services too, e.g. cross-flow condensers, kettle-type reboilers, etc. where heat transfer coefficient is not substantially depending by the flow rate. Allowing the unrestricted shell-side flow thanks to the open structure, potential vibrations phenomena induced by phase transition are prevented, again allowing for a possible increase of

Concerns may apply to the shell-side fluid entrance region: here the flow suddenly changes from radial to longitudinal direction (vice versa at fluid exit), potentially stressing the tubes, specifically at bundle periphery as no annular space is left. Reducing the grids span in correspondence of the inlet/outlet nozzles, stronger tubes confinement can be configured as required to guarantee no vibrations. The use of an annular chamber to distribute the flow entrance in homogeneous way through the full bundle circumference, further to provide an impingement protection to the directly exposed tubes, ensures at the same time the development of the longitudinal flow through the complete shell section since the first baffle pass.

vibrations due to his longitudinal flow design (**Figure 11**).

*Heat Transfer - Design, Experimentation and Applications*

shell side flow rate within the same exchanger constrains.

*EMbaffle® exploiting of the full shell area in comparison to NTIW in gas applications.*

Thanks to the strong bundle consistency and the full confinement of all tubes at any grid, EMbaffle® makes use of the full tube layout ensuring the filling of the complete shell section with consequent reduction of the equipment diameter and/or improved heat exchanger performance, while suppressing the risk of acoustic

The natural frequency of the tubes depends on the tube diameter and thickness, tube material and unsupported tube span, according to the following formula [4]:

> *WeL*<sup>4</sup> <sup>0</sup>*:*<sup>5</sup>

(14)

side Gas service heat exchangers).

minimum value that can be reached.

and consequent vibration.

**Figure 11.**

**334**

Dedicated CFD analysis has been performed to study different annular distributor configurations aimed to optimize the fluid-dynamics through the distributor and reduce the relevant correlated pressure drops (**Figure 12**).

Several geometries were modeled in order to analyze the flow distribution and the performances of each case. The flow velocity distribution at the inlet nozzle is showing a large area of the annular distributor to be interested by flow recirculation, addressing the flow to concentrate on lateral and bottom sides, trend accentuated by clearance reduction.

Decreased Top to Bottom exchanger slots size, contrary to what it could be expected, seems to address to a better uniform flow speed trend, but the dispersion of the flow rates at the entrance cannot be avoided. The average pressure drops are not significantly impacted by the shape of the cut and this supports the simplest and cheapest construction solution of the annular inner shell.

Thanks to all above provisions, no relative motion between tube and grid is permitted and, therefore, no wearing nor fretting is observed and reported after years of continuous operations in potential vibration services.

## **8. Fouling in EMbaffle®**

EMbaffle technology was originally conceived to enhance the shell side heat transfer by reducing fouling in heat exchange specific applications in refineries and petrochemical plants. By creating a uniform flow in the bundle, dead zones are omitted. By supporting the tubes using expanded metal grid the boundary layer is continuously interrupted thanks to the local increased velocity. By this approach the balance between fouling disposition and removal results at a lower fouling layer than in conventional heat exchangers.

EMbaffle® technology has then been applied to a variety of processes, where complexity of fouling mechanisms does not allow a predictable behavior. Further to the preliminary experimental results coming from authoritative Bodies, the actual performances in fouling reduction are finding systematic confirmation by the outcomes from a number of units installed and operating for several years.

Detailed monitoring of fouling development and study of growing rate had been originally concentrated on crude oil application, where fouling is strongly impacting the thermal and hydraulic performances of the exchangers. The overall heat transfer coefficient over time of a segmental baffle type heat exchanger and the same

exchanger with EMbaffle replacement bundle, have been monitored, adjusting shell side velocity and pressure drops in order to reproduce close process parameters for the two measurement campaigns.

**Figures 13** and **14** report the plotted measurements and the related fitted distributions showing, over the constantly higher value, the quicker decay of the OHTC as a clear indication of the higher fouling grow rate of the segmental baffle exchanger.

From the measurements, the overall fouling factors can be extrapolated by using the following model:

$$U(t) = U\_{\infty} + (U\_0 - U\_{\infty})e^{-\left[\frac{t-t\_0}{t\_f}\right]} \tag{15}$$

The fouling rate is derived from:

$$R(t) = \frac{1}{U(t)} - \frac{1}{h\_i} \frac{D\_o}{D\_i} - \frac{D\_o}{2\lambda} \ln\left(\frac{D\_o}{D\_i}\right) - \frac{1}{h\_o} \tag{16}$$

The following equation is used to calculate the maximum economic benefit connected with the ratio between the run time and number of cleaning steps

*QEdt* � *NcCcl* (17)

ð*tF* 0

In **Figure 17**, the economic benefit for a real case evaluated by comparing EMbaffle® performance with a parallel conventional unit on a base of 48 months operation is represented. Similar figures are of help in developing the best shutdown time at the light of the global plant configuration and performance.

*Comparison of overall heat duty performance of the EMbaffle® (dashed line) and the segmental baffle (solid*

*obj* ¼ *CE*

*Overall fouling factors plot for the EMbaffle® and segmental baffle heat exchanger bundles [6].*

Integral is calculated for the selected operating time.

*EMbaffle® Heat Transfer Technology Step-Up in CO2 Reduction*

*DOI: http://dx.doi.org/10.5772/intechopen.96253*

**Figure 15.**

**Figure 16.**

**337**

*line) heat exchanger bundles [7].*

The large variation in the early phase of both the segmental as of the EMbaffle run is reflected in the first part of the fouling plot. On the longer run the fouling of the EMbaffle is increasing relatively slow (**Figure 15**).

In order to assign the right value to exchanger performances, the method of optimum clean out time is used, where the optimum run time of the heat exchanger is based on cost evaluation, i.e. cost of decreased performance versus the cost of a clean-out (**Figure 16**).

**Figure 13.** *OHTC plot for the segmental baffle heat exchanger bundle [6].*

**Figure 14.** *OHTC plot for the EMbaffle® heat exchanger bundle [6].*

*EMbaffle® Heat Transfer Technology Step-Up in CO2 Reduction DOI: http://dx.doi.org/10.5772/intechopen.96253*

**Figure 15.**

exchanger with EMbaffle replacement bundle, have been monitored, adjusting shell side velocity and pressure drops in order to reproduce close process parameters for

**Figures 13** and **14** report the plotted measurements and the related fitted distributions showing, over the constantly higher value, the quicker decay of the OHTC as a clear indication of the higher fouling grow rate of the segmental baffle exchanger. From the measurements, the overall fouling factors can be extrapolated by using

> � *<sup>t</sup>*�*<sup>t</sup>* 0 *t f* h i

> > � 1 *ho*

(15)

(16)

*U t*ðÞ¼ *U*<sup>∞</sup> þ ð Þ *U*<sup>0</sup> � *U*<sup>∞</sup> *e*

� *Do*

The large variation in the early phase of both the segmental as of the EMbaffle run is reflected in the first part of the fouling plot. On the longer run the fouling of

In order to assign the right value to exchanger performances, the method of optimum clean out time is used, where the optimum run time of the heat exchanger is based on cost evaluation, i.e. cost of decreased performance versus the cost of a

<sup>2</sup>*<sup>λ</sup> ln Do Di* � �

the two measurement campaigns.

*Heat Transfer - Design, Experimentation and Applications*

The fouling rate is derived from:

*R t*ðÞ¼ <sup>1</sup>

the EMbaffle is increasing relatively slow (**Figure 15**).

*OHTC plot for the segmental baffle heat exchanger bundle [6].*

*OHTC plot for the EMbaffle® heat exchanger bundle [6].*

*U t*ð Þ � <sup>1</sup> *hi Do Di*

the following model:

clean-out (**Figure 16**).

**Figure 13.**

**Figure 14.**

**336**

*Overall fouling factors plot for the EMbaffle® and segmental baffle heat exchanger bundles [6].*

The following equation is used to calculate the maximum economic benefit connected with the ratio between the run time and number of cleaning steps

$$obj = C\_E \int\_0^{t\_F} Q\_E dt - N\_c C\_{cl} \tag{17}$$

Integral is calculated for the selected operating time.

In **Figure 17**, the economic benefit for a real case evaluated by comparing EMbaffle® performance with a parallel conventional unit on a base of 48 months operation is represented. Similar figures are of help in developing the best shutdown time at the light of the global plant configuration and performance.

**Figure 16.**

*Comparison of overall heat duty performance of the EMbaffle® (dashed line) and the segmental baffle (solid line) heat exchanger bundles [7].*

**Figure 17.** *Comparison of energy recovered (US\$) using EMbaffle® vs. segmental S&T in a crude preheating unit [7].*

### **9. Advancement in EMbaffle® design**

Finned tubes are widely used when equipment size and weight reduction play an important role. EMbaffle® developed a dedicated low fin "enhanced tube" helical profile (profile and finning process under patenting), conceived to fit longitudinal flow design aimed to increase the heat transfer based on two mechanisms: increase of active external tube surface and promotion of turbulence.

Two interesting cases of fin application have been addressed and will be presented in following paragraphs: gas cooling and oil to molten salts heat transfer in CSP applications.

#### **9.1 Gas cooling**

Several experimental measurements have been taken to check the EMbaffle® correlations precision in predicting the global heat transfer coefficient for gas cooling with plain tubes.

Water flow rate at the tube side has been sized to grant a ten times higher tube side coefficient with respect to the predictable shell side coefficient, so that changes in exchanger performance can be attributed to shell side heat transfer only.

In **Figure 18**, the correspondence between the correlations predictions and the experimental measures is reported: the theoretical curve fits perfectly with the measured temperature values, with predicted outlet temperatures differing less than 1%.

Achieving a further significant reduction in the overall required tubes number and therefore of the equipment dimensions, the EMbaffle® finned tubes exchanger design is expected to prove successfully especially in offshore applications where

More in general, the technology has a relevant impact on equipment costs containment for almost gas–gas and gas cooling processes and further tests shall be conducted to grant the continuous improvement of the performances in all gas

*Experimental data for gas cooling application: Comparison between EMbaffle® proprietary low fin tubes*

*Experimental data for gas cooling application: Comparison between experimental data versus correlations*

*EMbaffle® Heat Transfer Technology Step-Up in CO2 Reduction*

*DOI: http://dx.doi.org/10.5772/intechopen.96253*

Where tube-side can be the limiting factor, the use of enhanced features (inserts, inner surface micro-fins, etc.), to be applied in combination with shell side EMbaffle® grids, further to enhance the heat transfer, may also contribute to mitigate the fouling deposition on tubes side. The benefit of this combined

compactness and lightness are of the essence.

applications.

**339**

**Figure 19.**

*design vs. plain tubes.*

**Figure 18.**

*prediction for plain tubes.*

In **Figure 19**, experimental data to compare finned against plain tubes heat transfer performances are reported. In test case, the outlet air temperature reduces from 51 °C of the plain tubes case to 43 °C for the finned case, showing a significant improvement in heat transfer and global duty.

In the finned tubes test case, the air outlet temperature recorded for the plain tubes case has been reached at approx. 70% of the total tube length, showing a potential 30% tube length reduction.

These data allow to perform a design of the exchanger making use of the finned tube standard correlations to predict the temperature distribution profile and validate the global heat transferred.

*EMbaffle® Heat Transfer Technology Step-Up in CO2 Reduction DOI: http://dx.doi.org/10.5772/intechopen.96253*

#### **Figure 18.**

**9. Advancement in EMbaffle® design**

*Heat Transfer - Design, Experimentation and Applications*

improvement in heat transfer and global duty.

potential 30% tube length reduction.

date the global heat transferred.

in CSP applications.

cooling with plain tubes.

**9.1 Gas cooling**

**Figure 17.**

than 1%.

**338**

active external tube surface and promotion of turbulence.

Finned tubes are widely used when equipment size and weight reduction play an important role. EMbaffle® developed a dedicated low fin "enhanced tube" helical profile (profile and finning process under patenting), conceived to fit longitudinal flow design aimed to increase the heat transfer based on two mechanisms: increase of

*Comparison of energy recovered (US\$) using EMbaffle® vs. segmental S&T in a crude preheating unit [7].*

Two interesting cases of fin application have been addressed and will be presented in following paragraphs: gas cooling and oil to molten salts heat transfer

Several experimental measurements have been taken to check the EMbaffle® correlations precision in predicting the global heat transfer coefficient for gas

Water flow rate at the tube side has been sized to grant a ten times higher tube side coefficient with respect to the predictable shell side coefficient, so that changes

In **Figure 18**, the correspondence between the correlations predictions and the experimental measures is reported: the theoretical curve fits perfectly with the measured temperature values, with predicted outlet temperatures differing less

In **Figure 19**, experimental data to compare finned against plain tubes heat transfer performances are reported. In test case, the outlet air temperature reduces from 51 °C of the plain tubes case to 43 °C for the finned case, showing a significant

In the finned tubes test case, the air outlet temperature recorded for the plain tubes case has been reached at approx. 70% of the total tube length, showing a

These data allow to perform a design of the exchanger making use of the finned tube standard correlations to predict the temperature distribution profile and vali-

in exchanger performance can be attributed to shell side heat transfer only.

*Experimental data for gas cooling application: Comparison between experimental data versus correlations prediction for plain tubes.*

#### **Figure 19.**

*Experimental data for gas cooling application: Comparison between EMbaffle® proprietary low fin tubes design vs. plain tubes.*

Achieving a further significant reduction in the overall required tubes number and therefore of the equipment dimensions, the EMbaffle® finned tubes exchanger design is expected to prove successfully especially in offshore applications where compactness and lightness are of the essence.

More in general, the technology has a relevant impact on equipment costs containment for almost gas–gas and gas cooling processes and further tests shall be conducted to grant the continuous improvement of the performances in all gas applications.

Where tube-side can be the limiting factor, the use of enhanced features (inserts, inner surface micro-fins, etc.), to be applied in combination with shell side EMbaffle® grids, further to enhance the heat transfer, may also contribute to mitigate the fouling deposition on tubes side. The benefit of this combined

approach is therefore not only the increased heat recovery but also prolonged exchanger operating time through the reduction of fouling progress on both shell and tube sides.

Other than confirming the good corrosion resistance of grid material in critical ambient conditions registered with standard corrosion tests formerly performed, it gives solid confirmation to the mechanical strength of the grid excluding at the same time any potential erosion defect on exchanger tubes surface in all EMbaffle technology application. This is of course further supported by the several years of service of the EMbaffle exchangers in different process services without reporting

Few design cases are presented in this paragraph as examples of how the appli-

Two identical units (each one with two exchangers in parallel) have been installed in a platform. Using Sea water, the Overhead Gas Coolers were designed to

For this process the temperature approach between the fluids dictated a pure countercurrent arrangement, and the high water flow rate on the shell side did not allow the use of an F-shell TEMA type. Consequently a conventional segmental design in this case would have resulted in a much bigger and not-optimized geometry. A single pass for both tube and shell side exchanger would have been applied,

The very limited shell-side available pressure drop in combination with the ability to accommodate large flow rates made this application very suitable for EMbaffle®, making possible the use of a F-shell TEMA type (**Figure 20**). The result was an optimized design, able to achieve a pure counter current arrangement with the application of U-tubes, which granted a single tube sheet per exchanger, reducing the weight. During the design stage a higher OHTC has been also exploited, with a consequent reduction in required heat transfer surface. Given the off-shore application, the reduction in size and weight obtained for the exchangers was particu-

grids and/or tubes defect.

larly beneficial.

**Figure 20.**

**341**

*EMbaffle® overhead gas cooler.*

**10. EMbaffle® design cases**

**10.1 DesignCase-1: overhead gas cooler**

cation of EMbaffle® technology brings evident benefits.

*EMbaffle® Heat Transfer Technology Step-Up in CO2 Reduction*

*DOI: http://dx.doi.org/10.5772/intechopen.96253*

cool high pressure acid natural gas from 110 °C down to 33 °C.

with straight tubes and two tube sheets per exchanger.

For applications such as LNG vaporization, the combination between EMbaffle® and tube inserts is expected to be quite effective. On shell side, the EMbaffle® open structure will prevent the formation of dead zones guaranteeing, with the selection of proper grids span, the required tubes support, while inserts can mitigate the vaporizing issues at tubes inner surface by increasing the radial mixing.

#### **9.2 Oil to molten salts in CSP**

A test campaign was carried out on the molten salt/thermal oil case to compare the performance between the use of bare tubes with finned tubes.

A heat exchanger based on EMbaffle technology with finned tubes was installed at the Concentrating Solar Platform centre in Almeria (Spain), the largest development and test center in Europe for molten salt application in CSP.

A test campaign was carried out using molten salt and thermal oil as media. A comparison has been made between the field test and an equivalent plain tube case calculated with the correlations.

Results shows an average 8% reduction in the overall heat transfer resistance. The consequent increase in performances is significant, even if not so high in absolute value: application of low fin tubes for this process shall be carefully evaluated.

#### **9.3 Mechanical performance test**

The use of baffles made with "metal grid" instead of the more common "metal plate" suggests the need to verify their mechanical strength characteristics, especially in cases finned tubes are used and in the presence of processes with repeated thermal transients.

The different temperature distribution between the bundle support cage and the tubes during thermal transient brings to sliding of the tube inside the grid mesh, which could result mechanically harmful especially in the case of finned tubes.

In addition to the FEA for checking the static and dynamic stresses due to the accelerations induced on the tubes and on the grid, an experimental test was carried out to verify the consequences onto the grid subjected to the periodic longitudinal displacement of finned tubes in the most stringent conditions.

Two vertical baffles were positioned inside a horizontal cylindrical chamber and a finned tube was passed through them; weight and dimensions of tube were representative of the real exchanger conditions. A servomotor and a screw-nut type transmission were used to move the tube by operating a mechanical arm designed to transfer only a horizontal movement, minimizing any vertical thrust. The cylindrical chamber was filled with molten salts kept liquid with a system of heating resistances to maintain a temperature constantly above 380 °C.

Horizontal oscillatory movements (5 mm) equivalent to a 10-years working period of a exchanger with two daily transients were simulated to evaluate the effects of the relative wearing between the exchanger tube fin diameter and contact support points of the baffle grid diamond.

At the end of the test period the measurements of the outer diameter of the finned surface did show variation in height of the fins within 5% while no evidence of surface defect was registered on the contact profile of the grid mesh. Such a result is of extreme importance.

*EMbaffle® Heat Transfer Technology Step-Up in CO2 Reduction DOI: http://dx.doi.org/10.5772/intechopen.96253*

Other than confirming the good corrosion resistance of grid material in critical ambient conditions registered with standard corrosion tests formerly performed, it gives solid confirmation to the mechanical strength of the grid excluding at the same time any potential erosion defect on exchanger tubes surface in all EMbaffle technology application. This is of course further supported by the several years of service of the EMbaffle exchangers in different process services without reporting grids and/or tubes defect.
