Material And Energy Balance In Biological Processes
Introduction
Mass and energy balances are crucial tools in bioprocess engineering analysis. The transfer of mass and energy within the bioprocessing system must be known and tracked in order to control and produce suitable desired products. The material and energy balances are highly important especially in food industries, they are fundamental to control the amount of yield of the products within the system and most importantly to control the overall process. All the food industries are extensively using the mass and energy balance as a tool to reduce the consumption of energy in the process thus reducing the cost of energy as much as possible. (Nzifst. org. nz, 2018)Material/ mass balance: The material balance also referred to as the mass balance is basically an application of conservation of mass to analyze bioengineering processes. This is done by accounting all the material that is entering and leaving the bioreactor.
The conservation of mass is basically a law which states that the mass cannot be created and it can also not be destroyed meaning that it can only be transformed or transferred from one point to the next. Without the material balance, it is difficult to measure the flow or transfer of mass within the system and without this tool the production of many biological products would be impossible to achieve because for any system to operate effectively a known amount of reactants together with biomass must be known and to also achieve the desired products a known amount of products must be removed, putting into account the amount of material that must be recycled and discarded from the system or added to carry out a steady process which is effective for the production of desired products.
The mass balance is greatly used in pilot plant experiments and without these material balances, it would not be possible to create and handle a process plant cautiously and efficient. (Guivarch and Hallegatte, 2012)
Mathematical modelling: Based on the law of conservation of mass, the total amount of the weight of all materials entering any system must be equivalent to the total amount of all the materials leaving the system associated with any accumulating material remaining in the process. This can be mathematically computed, refer to equation 1 below: Mass accumulated = mass in – mass out + mass generated – mass consumedIf the process is carried in a continuous system assuming that the process is in steady state by continuously adding reactants and continuously removing accumulates to maintain the steady state, then the mass accumulation becomes negligible: Mass accumulation = 0 Therefore: mass in + mass generated = mass out – mass consumed Also if there is no reaction taking place in the system, then this means that there will be no consumption of any reactants. If the is no consumption of the reactants its most probably that the biomass is not present in the system and thus there will be no mass generated.
Mass consumed= 0Mass generated= 0 Zero mass consumed and generated leads the mass balance equation to: Mass in = Mass outA system is usually composed of a reactor and a separator with streams connected for the flow of these materials. The system is also isolated from the external environment by a system boundary. The stream which passes through the boundary and connects with the reactor to transfer products is referred to as the feed steam. If the system contains more than one vessel, then the vessels are connected by a stream called the intermediate stream. Then the stream that passes out the boundary carrying products out is either the product stream or the purge stream. And lastly there is a stream which connects the downstream back to the feed stream and it is known as the recycle stream. (Feinberg and Ellison, 2001)Mass feedback (recycle): Mass systems can also be achieved on systems that have recycling flows.
These systems are constructed in such a way that their output streams are connected to the feed stream in which some of the products in down streams are pumped back to the feed as reactants to be converted again. Differential mass balance: There are differential mass balances which are used to generate differential equations to improve and make the mass balance tool more effective. There systems which are good examples of the application of differential mass balance and these systems include: Batch system-Semi-continuous system-Continuous system-Purge stream: Energy balance.
