Claims:1. A process for drying algal bio-mass, said process comprising the following steps:
- determining the rheological characteristics of said algal bio-mass; and
- drying said algal bio-mass in one of a ring dryer, a flash dryer, or a fluidized bed dryer, if said algal bio-mass demonstrates non-Newtonian rheology.
2. The process as claimed in claim 1, wherein said algal bio-mass demonstrating Newtonian rheology is dried in spray dryer.
3. The process as claimed in claim 1, wherein said process further comprises the following steps:
- converting said non-Newtonian algal bio-mass to Newtonian algal bio-mass by adding a fluid medium to said non-Newtonian algal bio-mass; and
- drying said Newtonian algal bio-mass in said spray dryer;
wherein said fluid medium is water.
4. The process as claimed in claim 1, wherein said process further comprises the following steps:
- converting Newtonian algal bio-mass to fluidizable non-Newtonian algal bio-mass by adding a solid medium to said Newtonian algal bio-mass; and
- drying said non-Newtonian algal bio-mass in one of said ring dryer, flash dryer or fluidized bed dryer.
5. The process as claimed in claim 1, wherein said process further comprises the following steps:
- adding a solid medium to non-Newtonian algal bio-mass to further alter the non-Newtonian characteristics and fluidizability; and
- drying said non-Newtonian algal bio-mass in one of said ring dryer, flash dryer or fluidized bed dryer.
6. The process as claimed in claim 1, wherein said algal bio-mass is micro-algae.
7. The process as claimed in claim 1, wherein said spray dryer, said ring dryer, said flash dryer, and said fluidized bed dryer include a drying unit selected from the group consisting of conveyor (s), mixer (s), hot air generator (s), cyclone (s), classifier (s), duct(s), cage mill (s), blower (s), bag filter (s), and atomizer.
8. The process as claimed in claim 1, wherein said process includes an optional step of washing said algal bio-mass with water before drying.
9. The process as claimed in claim 1, wherein:
the hot air temperature within said spray dryer, said ring dryer, said flash dryer and said fluidized bed dryer ranges from 500 C to 2200 C; and
the feed solid content in said dryer ranges from 4% to 50%.

10. The process as claimed in claim 1, wherein the moisture present in the dried algal bio-mass varies in the range of 5% to 35%
, Description:FIELD
The present disclosure relates to processes for drying algal bio-mass.
BACKGROUND
In conventional processes, the rheological characteristics of the algal slurry are not considered in the selection and operation of the dryer. In the conventional approach, it is observed that by not considering the rheological characteristics lead to selection of inappropriate dryer, operational challenges, and inefficient operation of the dryer, thereby leading to huge operating cost and productivity loss. Furthermore, incorrect selection of a dryer, because of not considering rheological characteristics, leads to high energy consumption, capital cost, compromising on product quality and unit being unfit for desired drying operation.
Therefore, there is felt a need of a process for drying an algal bio-mass that enables effective selection of a dryer and alleviates above mentioned drawbacks.
OBJECTS
Some of the objects of the present disclosure, which at least one embodiment herein satisfies, are as follows:
An object of the present disclosure is to provide a process for drying algal bio-mass that carries out rheological characterization of algal slurry by rheometer which is observed to vary significantly depending upon method of the algal slurry preparation.
Another object of the present disclosure is to provide a process for drying algal bio-mass that considers rheological characteristics to select and operate a dryer for drying the algal bio-mass.
Another object of the present disclosure is to provide a process for drying algal bio-mass that enables effective selection and operation of a dryer for drying the algal bio-mass.
Yet another object of the present disclosure is to provide a process for drying algal bio-mass that enables selection of a dryer that consumes less energy for drying the algal bio-mass.
Other objects and advantages of the present disclosure will be more apparent from the following description, which is not intended to limit the scope of the present disclosure.
SUMMARY
The present disclosure envisages a process for drying algal bio-mass. The process comprises the following steps. The rheological characterization of the algal bio-mass to be dried is carried out. The rheological characteristics are used to determine whether the algal bio-mass is Newtonian slurry or non-Newtonian slurry. If the algal bio-mass is Newtonian slurry, the algal bio-mass is preferred to be dried in a spray dryer. If the algal bio-mass is non-Newtonian slurry, the algal bio-mass is dried in one of a ring dryer, a flash dryer or a fluidized bed dryer.
In one aspect, the non-Newtonian algal bio-mass is converted to Newtonian algal bio-mass by adding a fluid medium to the non-Newtonian algal bio-mass. The Newtonian algal bio-mass is then dried in the spray dryer to produce fine algal dry powder. Preferably, water is used as the fluid medium. However, in this process the thermal energy required to dry the algal biomass is high because of dilution to transform rheological characteristics.
In another aspect, the Newtonian algal bio-mass is converted to non-Newtonian algal bio-mass by adding the solid medium to the Newtonian algal bio-mass. Alternately, solid medium is also added to non-Newtonian algal bio-mass to further modify non-Newtonian rheology and fluidizability. The non-Newtonian algal bio-mass is then dried in one of the ring dryer, a flash dryer or fluidized bed dryer.
Typically, the algal bio-mass can be micro-algae.
In another embodiment, the spray dryer, ring dryer, flash dryer, or fluidized bed dryer include a drying unit that consist of (but not limited to) equipment selected from the group of conveyor(s), mixer(s), hot air generator(s), cyclone(s), classifier(s), duct(s), cage mill(s), blower(s), bag filter(s), heat exchanger(s), atomizer, and/or any additional process equipment as appropriate.
In a preferred embodiment, the hot air temperature within the spray dryer, the ring dryer, the flash dryer, and fluidized bed dryer ranges from 500 C to 2200 C.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
A process for drying an algal bio-mass, of the present invention, will now be described with the help of the accompanying drawing, in which:
Figure 1 illustrates the process of the present disclosure, in accordance with an embodiment of the present invention;
Figure 2 illustrates the process of the present disclosure, in accordance with another embodiment of the present invention;
Figure 3 illustrates a graphical representation of change in viscosity with respect to the shear rate for 20% wt centrifuged slurry and 20% wt dry powder based slurry;
Figure 4 illustrates a graphical representation of change in viscosity with respect to the shear rate for 5% wt centrifuged slurry and 5% wt dry powder based slurry; and
Figure 5 illustrates a graphical representation of change in viscosity with respect to the shear rate for 20% wt centrifuged slurry and 40% wt dry powder based slurry.
DETAILED DESCRIPTION
The present invention envisages a process for drying algal bio-mass that considers rheological characteristics of the algal bio-mass.
Typically, rheological characteristics include shear stress, and viscosity under varying shear rate. It is critical to carry out shear stress and viscosity characterization under varying shear rates to identify if the shear stress and viscosity varies with shear rate (shear thinning or shear thickening behavior) or remains constant with shear rate variation. It is identified in this disclosure that the rheological characteristics vary significantly with method of preparation of algal slurry.
The process of the present invention comprises the following steps. Initially, the rheological characteristics of the algal bio-mass to be dried are determined as a function of shear rate. For example, the determined viscosity variation with shear rate is further considered to determine whether the algal bio-mass is Newtonian slurry or non-Newtonian slurry. If the algal bio-mass is Newtonian slurry, the algal bio-mass is dried in a spray dryer. If the algal bio-mass is non-Newtonian slurry, the algal bio-mass is dried in one of a ring dryer or a flash dryer or fluidized bed dryer.
A situation is considered where a spray dryer is wrongly installed at downstream of a centrifuge that produces highly non-Newtonian algal slurry. Further, as non-Newtonian slurry with high viscosity is not preferred in a spray dryer, the process is further modified to include following steps which enable the non-Newtonian algal bio-mass to be effectively dried in the spray dryer. The non-Newtonian algal bio-mass is converted to Newtonian algal bio-mass by adding a fluid medium to the non-Newtonian algal bio-mass from centrifuge as illustrated in figure 1. However, in this process the thermal energy required to dry the algal biomass is high because of dilution to transform rheological characteristics. The Newtonian algal bio-mass is then dried in the spray dryer. Preferably, water is used as the fluid medium.
With reference to figure 1, a fluid medium 2, preferably water, is added to a non-Newtonian centrifuged algal bio-mass 1 to form a mixture 3 in a mixer 100. The mixture 3, which is now Newtonian slurry, is fed to a spray dryer 102. The spray dryer produces dry powder 5.
Furthermore, as Newtonian or non-Newtonian algal slurry may not be effectively fluidized and dried in a ring or a flash dryer or fluidized bed dryer, the process further comprises following steps which enable the Newtonian or non-Newtonian algal bio-mass to be effectively fluidized and dried in the ring or flash dryer or fluidized bed dryer. The Newtonian or non-Newtonian algal bio-mass is converted to fluidizable non-Newtonian algal bio-mass by adding a solid medium to algal bio-mass, as illustrated in figure 2. The fluidizable algal bio-mass is then dried in one of the ring dryer or flash dryer or spin flash dryer.
With reference to figure 2, a solid medium 2 (recycled dry powder), is added to a centrifuged algae bio-mass 1 to form a non-Newtonian fluidizable mixture 3 in a mixer 200. The mixture 3, which is now a non-Newtonian fluidizable material, is fed to a ring or flash dryer or fluidized bed dryer 202. Drying takes place in the ring or flash dryer or fluidized bed dryer 202 to generate dry powder 5.
In an embodiment, the feed solid content ranges from 4% to 50%.
The process of the present disclosure can potentially be used to determine the type of dryer selected from the group consisting of fluidized bed dryer, rotary dryer, drum dryer, tray dryer, lab oven, agitated thin film dryer, vacuum dryer, solar dryer or multi-stage combination of any such dryers for algae drying.
Typically, the algal bio-mass is micro-algae which is a heat sensitive material.
Although the present disclosure is described with reference to drying of micro-algae, drying of any organic or non-organic material is well within the scope and ambit of the present disclosure. The process, of the present disclosure, can also be adapted for selection of dryer for drying any organic or non-organic material therewithin.
In another embodiment, the spray dryer, ring dryer, fluidized bed dryer and flash dryer include a drying unit selected from the group consisting of conveyor(s), mixer(s), hot air generator(s), cyclone(s), classifier(s), duct(s), cage mill(s), blower(s), and bag filter(s), atomizer, and/or any appropriate equipment as required. The type of dryer is selected based on target aggregate size and product fineness.
In a preferred embodiment, the hot air temperature within the spray dryer, the ring dryer, the flash dryer and fluidized bed dryer ranges from 500 C to 2200 C.
In yet another embodiment, the process includes an optional step of washing the algal bio-mass with water before feeding to dryer. The centrifuged algal slurry being fed to dryer has soluble salt content below 5%. The algal bio-mass is de-agglomerated in cage mill or any other arrangement.
The process, of the present disclosure, considers rheological characterization like viscosity, shear stress under varying strain (measured using rheometer) in dryer selection, design and operation.
The process further considers fluidization and/or pneumatic conveying properties along with rheological & feed moisture content measurement information to select, design and control operation, and troubleshooting of the drying process.
The process also considers elemental analysis of algae, dry biomass quality aspects, proximate analysis and any other relevant component analysis, slurry pH, salinity information to determine the type of dryer.
Experiments have been performed at room temperature with 5% and 20% w/w slurry prepared by different methodologies. In first method, 20% concentrated slurry is utilized which is produced by centrifugation of cultivated algal biomass. In the second method, reconstituted slurry is utilized which is produced by mixing dry algae powder with water. A comparison of viscosity with shear rate is described below with reference to figure 3, figure 4, and figure 5.
With reference to figure 3, it is observed that viscosity drops significantly with increasing shear rate. For a centrifuged slurry (20% concentration), viscosity drops from about 107 cP to about 2000 cP with increase in shear rate from 0.07 s-1 to 32 s-1. For slurry prepared from dry powder, viscosity drops from about 104 cP to 733 cP with increase in shear rate from 0.06 to 40 s-1. It can be observed from figure 3, that the viscosity of the slurry prepared from dry powder is about 1000 times lower than the centrifuged slurry at low share rate (<0.1s-1) and hence, is a strong function of the methodology of slurry preparation. Although solid content (and moisture content) remains same, viscosity values are significantly different. For the 20% dry powder based slurry, viscosity variation over studied range of shear rate is significantly lower (relatively flat), compared to that observed steep drop in viscosity for the 20% wt centrifuged slurry. This observation leads to the conclusion that 20% centrifuged slurry is significantly more non-Newtonian than 20% dry powder based slurry.
With reference to figure 4, it is observed that viscosity drops significantly with increasing the shear rate. For 5% centrifuged slurry, viscosity drops from 2983 cP to 4.6 cP with increase in shear rate from 0.07 s-1 to 442 s-1. Viscosity of 5% centrifuged slurry (as shown in figure 4) is several orders lower than the viscosity of 20% centrifuged slurry (as shown in figure 3). For 5% slurry prepared from dry powder, viscosity drops from 562 cP (at 0.01 s-1) to 3.3 cP (at 2.5 s-1) and then remains almost constant at higher shear rate. As seen, the viscosity of the slurry prepared from dry powder is lower than the centrifuged slurry and hence, is a strong function of the methodology of slurry preparation. It is clear from figure 4 that although solid content (and moisture content) remains same, viscosity of the samples are significantly different.
During the studies, it is observed that it is a difficult task to mechanically (by centrifugation) dewater the system above 20% solid. However, slurry with more solid loading (40% solid in this example) can be prepared by addition of water in dry powder or by adding dry powder in relatively dilute slurry.
With reference to figure 5, a comparable rheological behavior is observed for 20% centrifuged slurry and 40% dry powder based slurry. It can be concluded from the measurement of rheological characteristics of the 20% centrifuged slurry and 40% dry powder based slurry that for similar solid content, centrifuged material has higher viscosity as compared to that of the dry powder based slurry.
Further, it is also observed that, in a spray dryer installation, non-Newtonian feed slurry needs dilution to make proper rheology control. In ring/flash dryer or fluidized bed dryer installation, Newtonian slurry can not be processed and requires rheology modification to improve fluidizability to enable the material to be processed.
The process, of the present disclosure, considers rheological characteristics of the algal slurry in order to select a proper dryer for drying the algal slurry. A spray dryer is a better choice for drying operation of algal bio-mass which behaves as Newtonian slurry. The spray dryer tends to choke or create serious maintenance issues, when drying of highly viscous non-Newtonian algal slurry is carried therewithin. Further, a ring dryer or a flash dryer or fluidized bed dryer is a better choice for drying operation of highly viscous algal bio-mass which behaves as non-Newtonian slurry.
The present invention is further described below for illustration purpose only and not to be construed for limiting the scope of the disclosure. These processes can be scaled up to industrial/commercial scale and the results obtained can be extrapolated to industrial/commercial scale.
Case 1: Drying of highly viscous 20% algal bio-mass in a spray dryer
For drying highly viscous 20% algal bio-mass in a spray dryer, water is added in the centrifuged slurry (non-Newtonian) to prepare dilute slurry with Newtonian rheology. The slurry was further dried in a spray dryer. The process is illustrated in figure 1. Mass flow across each stream is presented in Table 1. For evaporative load of 378.49 kg, latent heat for water evaporation is 855.73 MJ. Considering thermal efficiency of 40% in spray dryer, heat energy required to dry the algal slurry is 2139.32 MJ.
Stream 1 2 3 4 5
Total, kg 100.00 300.00 400.00 378.49 21.51
MAF Algae, kg 17.57 17.57 17.57
Ash, kg 2.43 2.43 2.43
Water, kg 80.00 300.00 380.00 378.49 1.51
Table 1: Components in different stream (basis 100 kg centrifuged slurry) during spray drying
Case 2: Drying of highly viscous 20% algal bio-mass in a ring dryer
It is difficult to air lift 20% centrifuged algal slurry in a cage mill of the ring dryer. Algal slurry prepared by adding dry powder in water has significantly lower viscosity compared to 20% centrifuged slurry that is never dried. Such algal bio-mass with lower viscosity is not appropriate material for directly feeding to ring dryer without appropriate rheology modification, as such algal bio-mass cannot be fluidized in the ring dryer. Table 2 illustrates fluidization behavior of centrifuged algal slurry at air velocity of about 8 m/s and air temperature of 1800C. Centrifuged and washed algae having not more than 0.6% salinity was used as feed to dryer.
Material Fluidizability & ability to be pneumatically conveyed
Centrifuged slurry (15% solid) No
Centrifuged slurry (15% solid) and recycled powder (7% moisture) mixture in 6.8:1 ratio Yes
Centrifuged slurry (20% solid) No
Centrifuged slurry (20% solid) and recycled powder (7% moisture) mixture in 13.6:1 ratio Yes
Table 2: Pretreatment for modification of rheology and fluidization properties
Solid powder was added in centrifuged slurry and mixed properly to prepare proper mixture that can be processed in ring dryer. In this case, solid powder was added in the centrifuged slurry (non-Newtonian) to prepare fluidizable mixture in ring dryer operating condition. The process is illustrated schematically in figure 2. Mass flow across each stream is presented in Table 3.

Stream 1 2 3 4 5
Total, kg 100.00 17.66 117.66 78.49 21.51
MAF Algae, kg 17.57 14.42 31.99 0 17.57
Ash, kg 2.43 2.00 4.43 0 2.43
Water, kg 80.00 1.24 81.24 78.49 1.51
Table 3: Components in different stream (basis 100 kg centrifuged slurry) during ring drying
For evaporative load of 78.49 kg, latent heat for water evaporation is 177.47 MJ. Considering thermal efficiency of 40% in dryer, heat energy required to dry the material in the ring dryer is 443.67 MJ which is significantly lower than heat energy required to dry the algal bio-mass in the spray dryer which is 2139.32 MJ.
Therefore, it is observed that because of inappropriate choice of the dryer (which did not consider appropriate rheological aspects during design and operation), significant wastage of heat energy takes place.
Dry algae powder, produced by the dryer selected as per the process illustrated in the present disclosure, demonstrates hygroscopic behavior when exposed to ambient condition. Table 4 demonstrates the increase in moisture content with respect to time when the dry powder was exposed to ambient condition (260 C and 76% relative humidity). Based on the end application of dry powder and its storage condition, end point in drying is determined. For example, if the powder needs to be stored under ambient condition for the application at hand, then excessive drying upto 7% moisture content is not required. In such case, moisture content upto 12.6% at dryer exit is sufficient. Lower moisture content in dryer is derived from more drying energy and drying time. Alternately, if dry powder application requires 7% moisture in the dry powder, then post drying, material needs to be stored under sealed moisture free condition. Further, the end point and hygroscopic behavior depends strongly on type of algal species.
Time, hr % moisture
0 7.0
18 9.0
90 12.6
185 12.6

Table 4: Change in moisture content with exposure to ambient condition
It is observed that the moisture in the algal bio-mass dried in a dryer selected by adapting the process of the present disclosure varies in the range of 5% to 35%.
The process described in the present invention prevents wrong selection of dryer, and enables selection of energy efficient drying process. Further, the process ensures smoother operation of the dryer.
TECHNICAL ADVANCEMENTS
The present invention described herein above has several technical advantages including, but not limited to, the realization of a process for drying algal bio-mass that:
• considers rheological characterization using rheometer to select and operate a dryer for drying the algal bio-mass;
• enables effective selection and operation of a dryer for drying the algal bio-mass; and
• enables selection and operation of a dryer that consumes less energy for drying the algal bio-mass.
The disclosure has been described with reference to the accompanying embodiments which do not limit the scope and ambit of the disclosure. The description provided is purely by way of example and illustration.
The embodiments herein and the various features and advantageous details thereof are explained with reference to the non-limiting embodiments in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.
The foregoing description of the specific embodiments so fully revealed the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.
Throughout this specification the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.
The use of the expression “at least” or “at least one” suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the disclosure to achieve one or more of the desired objects or results.
Any discussion of documents, acts, materials, devices, articles or the like that has been included in this specification is solely for the purpose of providing a context for the disclosure. It is not to be taken as an admission that any or all of these matters form a part of the prior art base or were common general knowledge in the field relevant to the disclosure as it existed anywhere before the priority date of this application.
The numerical values mentioned for the various physical parameters, dimensions or quantities are only approximations and it is envisaged that the values higher/lower than the numerical values assigned to the parameters, dimensions or quantities fall within the scope of the disclosure, unless there is a statement in the specification specific to the contrary.
While considerable emphasis has been placed herein on the components and component parts of the preferred embodiments, it will be appreciated that many embodiments can be made and that many changes can be made in the preferred embodiments without departing from the principles of the disclosure. These and other changes in the preferred embodiment as well as other embodiments of the disclosure will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the disclosure and not as a limitation.