In-ground Molasses Storage Facility: Insights on the conventional and alternative molas...

In-ground Molasses Storage Facility: Insights on the conventional and alternative molas...: Molasses are sweet, viscous by-product primarily produced in the sugar milling and refining operations. Typically, the following are its ...

Insights on the conventional and alternative molasses storage

Molasses are sweet, viscous by-product primarily produced in the sugar milling and refining operations. Typically, the following are its main analyses as sourced from Sugar Regulatory Administration: Density ranging from 1400 – 1450 kg /cubic meter; Total Sugar as Invert (TSAI) ranges 45 – 50 %; and Production Temperature is normally at 60 degree Celsius.

Based from actual interviews from people who have sufficient knowledge in this field, molasses production constitutes a range of 3 - 4.5 % of the total raw sugar produced, which by practice, an indicative mean value of 3.6 % is normally used.

As sugar industry keeps its pace in the blooming state, the storage of such by-product become a concern. The reason is primarily due to a wide range of applications that can be processed using this by-product as an input material. Industrial applications such as binding agent, stabilizer, chelating agent, fertilizer stuff, are some to name a few of its industrial utilization.

Basically, molasses are used for alcohol fermentation which is further applied either for potable use or for gasoline blending preparations. This also gives significant use for animal feed manufacture due to its high energy content and palatability.

The concern now is in storing the molasses. Conventionally, sugar companies in the Philippines are using the above ground steel tanks for storage. This is the very common type of containment method that is practiced since then. Molasses which are collected from centrifugation of cane juice after undergoing cascading processes, are transported by pipes to either cooling systems or other heat mediators to achieve acceptable temperature prior to storage. This is done to ensure that no hot spots catered by the exothermic Maillard Reaction will occur once the molasses are impounded inside the tank. 

Alternatively, the development of polymeric geomembrane materials gave advent to the viability of an option of storing these molasses. In contradiction to the above ground system, this application is catered employing in-ground method of containment (where excavated earthen trough is lined with HDPE material of desired thickness and is equipped with a floating cover tailored with proper design and engineering). 

STORING IT THE CONVENTIONAL WAY...

Professional feedback regarding the use of above ground storage system turns its wheel on the costing and possible corrosion problems that may arise in a long run of the process. Specifically, these tanks are made up of mild steels of varying thickness and are ready bent  for the purpose of staggered in-site welding methodologies. The thickest metal plates are used for the base/bottom part while the thinner ones are applied in the upper part where pressure is fairly low. 

Volume of the tanks can be varied depending on the production of the mill. By operational protocol, however, a head space or volume allowance is provided should frothing or foaming occur during the storage phase. Technically, good engineering design can address this particular setback. Water shower can also be introduced in a fair amount to eliminate the frothing on top. 

Cooling system also varies from one application to another. Other tank storage abroad employs molasses cooling towers as integral part of the cooling system. External washing down of water to the tanks is also practiced by others whose storage tanks are considerably smaller in size. Others prefer aeration and air injection while some prefer just recycle streams to make sure that molasses temperature does not deviate from the normal acceptable limit.

Tanks necessitates several add-in constructions like providing a plinth for its base, bunding walls, mesh wires for the air vents, aerator motors, recycle stream pipes, etc. It also requires appropriate operation and maintenance since its serviceability and economic life is highly dependent on the given care of maintenance.

Internal and external corrosion may also pose possible risk for the tank. Dust and other external radicals can initiate rusting on the outside tank's structure which when neglected can be a serious corrosion threat. Accumulated moist as a result of localized condensation inside the tank can also be a factor for internal corrosion and worst when neglected, can drop the pH and ferment the stored molasses in untimely situation. 

And most importantly, the overall fabrication and installation of steel tanks is quite expensive. And O&M practices may as well allocate certain budget for periodic repainting and coating refurbishments.

THE ALTERNATIVE WAY...

There are several sugar industries abroad employing the alternative way of storage system for the cold molasses used for ethanol production and animal feeds. This system includes an excavated trough which is propped up with lining systems and a floating cover. The following are the installation elements of the in-ground storage method:

     Initial In-site Survey   -   the engineering and construction team commences an initial

                                               site visit to acquire glimpse on the construction viability. This 

                                               includes site topographical study like soil assessment, water 

                                               table level determination and foundation investigation

     Planning and Materials

                                          -   Appropriate polymeric geomembranes are proposed chiefly 

                                              constituted of polyethylene or polypropylene based materials.

                                              These materials are technically catered for a matched 

                                              application depending on the nature of soil to which they are

                                               exclusively engineered. Bottom/base depression alignments,

                                               canal systems, and sloping features are well planned and pre-

                                               commissioned.

     Welding methodologies

                                          -   Installation is carried out by utilizing automatic welding 

                                              equipment which are devised with heating elements for the

                                              fusing applications. This is normally undertaken 

                                              accompanying tests to ensure that welding is at standard.

     Floating Cover Engineering

                                          -   Roofing system is mechanized with alternating floats and weight

                                              arrayed across the width of the cover. This design allows 

                                              effective rainwater collection and shorter inside gas transport.

                                              Such design also provides shear-free motion of molasses as it is

                                              pumped in between the cover and liner. Desired folding and

                                              attachment schemes are structured to guarantee standard

                                              construction. Air venting systems are also designed to 

                                              compensate for the degassing procedure. This system works

                                               in a dual purpose mechanism: efficient air removal system and

                                               elimination of water incursion for the stored molasses.

Summing it all up, these two methods of storing molasses depicts almost similar mechanisms and operations when it comes to the engineering side. The only difference lies on these insights:

- Above ground steel tanks are EXPENSIVE in terms of fabrication yet needs smaller land area for its installation.

-In-ground storage of molasses requires bigger land area/footprint for its installation but CHEAPER as compared to steel tanks.