Operational Framework of Chemical Process Industries (CPI)
The primary objective of any chemical process industry is to convert raw material in valuable and useful final finished products. We cannot convert raw material directly into the final product, there area several intermediate steps which needs to be carried out to convert raw material into final finished product which is directly used in another industries or directly consumed by end user. Some of the steps may be easy and some of the processing steps are complex. Main processing steps involved in chemical process industry are shown in below diagram.
Figure 1: Processing Steps
Above diagram shows general steps and not applicable for all
the chemical processing industries, it varies industry wise. Some industries
may have additional processing steps and some steps may be omitted in some
industries which is shown in above figure.
Step 1: Raw Material Storage: To produce any product, the basic requirement is
raw material, without the raw material we cannot produce products. Sometimes it
can be supplied to plant from the nearby plant if any plant is producing product
which can be directly used as raw material for our production plant. It may be supplied
to plant from plant which is located far from our plant and it may be
transported by road or rail. Sometimes raw materials can be imported from other
countries by ships (i.e. transportation LNG by large cargo ships). We should
store enough raw material so that if we are not able to get raw material for
some time than our production does not hamper. To store material, provision of
storage tank or silos are to be provided in chemical process plant. Different
types of storage tanks are installed to store liquid or gaseous raw material and
for storage of solid material silos are provided. For unloading of raw material
from tanker of ships to storage tanks, adequate unloading facilities are
provided for smooth unloading operation.
Step 2: Feed Preparation: We cannot utilize these raw material into the process
plant because it may contain some impurities which may damage process plant equipment,
sometimes it acts as poison for the catalyst which is used in the reactor and
deactivate the catalyst. Sometimes these impurities may react with other raw
material and forms byproduct which is undesirable. So, it is necessary to separate
out those impurities present in the raw material so it does not damage our
process equipment. If our raw material is solid and size is differing form our process
requirement so we need to install size reduction equipment (Crusher or Ball
mill) to fulfil our process plant requirement. Sometimes we purchase raw
material in liquid phase and store in the liquid phase (but we use raw material
in vapour phase) so we need to install liquid vaporizer. For example, in nitric
acid production plant, ammonia is used as a raw material and it is stored in
liquid phase but it is used in the gas phase in the process. So, It is
vaporised in vaporizer prior it enters to the ammonia oxidize(reactor).
Step 3: Reaction: This stage is the most
crucial step for any chemical processing industry. To carry out reaction
equipment used is known as reactor. Reactor is considered as heart of chemical
process industries. In reactor raw material is converted into valuable raw products.
Sometime along with main product some of the raw material which is fed to the
reactor is converted into byproduct. Sometime more than one raw materials are
mixed together and fed into the reactor. For example, in nitric acid production
plant ammonia vapor is mixed air and then fed to the ammonia oxidizer (Tubular
reactor).
Step 4: Product separation: As discussed in step 3, some side reactions are also happening in the reactor and it produce the undesirable byproducts. So, we need to separate these byproducts from our main products to meet consumer requirement. For that we need to use different types of separation techniques to purify our main product. For examples distillation, liquid-liquid extraction, Gas absorption, evaporation, adsorption, crystallization, drying are the methods used to purify our main product. For Example, in nitration on mono-chloro-benzene, we get four isomers of nitro-chloro-benzene (PNCB, MNCB, ONCB and DCNB). These four isomers are separated by the vacuum distillation followed by the crystallization. For separation of azeotropic mixture of water and hydrochloric acid, extractive distillation with concentrated sulfuric acid as entrainer. For concentration of fruit juice, evaporation is used.
Step 5: Purification: Sometime, the main product is converted into the desired
purity product according to the customer’s requirement before sale because the
requirement of the market is not the same, someone want the product with less
purity and someone want product with high purity. For example, in sulfuric acid
plant the concentration is sulfuric acid is decided based on the buyer. In
petroleum refinery the quality of gasolene, diesel and kerosene depends on the
end user.
Step 6: Product storage and logistics: After the above steps our final product
is ready to sell in the market. It is not possible that all the product that we
have produced in our plant is sold directly. Sometime the market demand is
higher than the production capacity and sometime the market demand zero. We
need to store the final finished product in somewhere in out plant. To store
the final finished product, we need storage tank so we can supply the product
to the market when the demand is high and we can store our product which is
produced in our plant when the demand zero. In oil refineries and petrochemical
plants separate plot area is provided and there are multiple tanks are
installed to store raw material and products. After storage, the material is
filled in drum or tankers for dispatch. If product is in solid form, then it
will be packed in the plastic bags (jumbo bags) or box. In large chemical process
plants, oil refineries and petrochemical complexes loading arm is used to load
product in tanker from tank farm.
A successful chemical process requires a balance between Unit
Processes (chemical changes in the reactor) and Unit Operations (physical
changes like separation and storage). As a professional in the field,
understanding that "Product Separation" and "Purification"
are often more energy-intensive than the reaction itself is key to optimizing
plant efficiency.
