(Tell me can you feel it?)
(Tell me can you feel it?)
The heat is on, the heat is on, the heat is on.

("The Heat is On," sung by Glenn Frey, 1993)

 

SOME CHEMICAL REACTIONS GENERATE HEAT
AND INCREASE PROCESS TEMPERATURE

PTOA Readers and Students who are reading the PTOA segments in the intended sequence already know that physical changes of state (aka: phase changes) that lead to a more-bound-together state will release heat into the surroundings while the phase change is ongoing.

A gas condensing into a liquid is an example of a change of state that results in a more-bound-together state.

There are also chemical changes that generate heat and increase the process temperature.

Chemically breaking up the bonds of feedstock components and rearranging their chemical structure to make more desirable products takes place in specialized processing equipment called reactors.

Exothermic reactions are reactions that release energy and generate heat.

A reactor that has an ongoing exothermic reaction is easy to identify: the process stream temperature of the products exiting the reactor outlet will be greater than the process stream temperature of the feedstocks that entered the reactor inlet.

Feedstocks entering a reactor are also called reactants.

Reactors and common industrial reactions will be thoroughly covered in future PTOA segments.

The first priority is to make certain that all PTOA Readers and Students understand how to interpret written chemical reactions and understand how they directly relate to the real world of industrial processing.

 

INTERPRETING WRITTEN CHEMICAL REACTIONS

Reactants/Reactor Feedstock
are on the Left Hand Side of the Reaction Arrow

The reactants appear on the left hand side of the arrow.

In the processing plant, the reactants are also the feedstocks that flow into the reactor inlet.  

Upgrading the reactants into more valuable, desired products is the reason the reactor was built.

Products/Reactor Effluent
are on the Right Hand Side of the Reaction

The products of the reaction appear on the right side of the arrow.

In real-word industrial processing, the reaction products are the products exiting the  reactor outlet.

The correct jargon for "reactor products" is reactor effluent. The reactor effluent still needs to be sent through equipment to separate out impurities before the desired product can be sold; calling the reactor effluent a final "product" would be inaccurate.

The graphic on the right shows that products of some reactions...like "C" and "E".... become reactants for other reactions. These products are called intermediate reaction products and in the real processing world: byproducts.

The plant is often called by the name of the desired reactor product.  For example, a "Hydrogen Plant" is operated to make mostly hydrogen; the "Naphtha Hydrotreater Plant" has a Naphtha Hydrotreater Reactor that hydrotreats naphtha.  Makes sense, eh?

 

Application to Real-World Processing

In the above graphic, the familiar Steam Methane Reforming (SMR) reaction is the top reaction. PTOA Readers and Students already know that the SMR reaction is a popular processing technology used to make hydrogen (H2) from steam (H2O) and methane (CH4) .

The middle reaction on the chart is the Water-Gas Shift reaction.

The Water Gas shift reaction uses steam (H20) to convert carbon monoxide (CO) into carbon dioxide (CO2) and makes more of the desired product, hydrogen (H2).

Since the overall yield of hydrogen (H2) increases by adding the Water Gas Shift reaction, industrial hydrogen plants will include the technologies for both of the reactions in their Hydrogen Plants.

The third reaction is a Combustion Reaction.

PTOA Readers and Students are already familiar with this reaction; this reaction takes place in fired heaters and boilers that combust natural gas (CH4, methane) to generate the combustion gases that indirectly heat the fluids flowing through the heater and boiler tubes.

 

Real-World Intermediate By Products

The carbon monoxide (CO) reactant in the Water-Gas Shift reaction was a product that was made in the Steam Methane Reaction.

The carbon monoxide (CO) is an intermediate chemical reaction product; in the processing world the CO would be called a less desirable byproduct made in the SMR reaction.

When a chemical reaction is involved, there will always be byproducts of lesser value. Sometimes the byproducts have no value at all and take up valuable space in the reactor.

 Process Operators and Control Board Operators are responsible for operating a catalytic reaction to produce more of the desired product and less of the byproducts.

Chemical Reaction Arrows

The chemical reaction arrows typically point to the right...to the desired products...as shown in the Combustion Reaction that appears on the third line in the above schematic.

The Steam Methane Reforming Reaction and the Water Gas Shift Reaction have arrows going both ways.

This duo-arrow-pointing means that...under certain circumstances... the reaction can go either way; the reactants can become products and vice versa.

The purpose of controlling reaction temperatures, reaction pressures, and reactant flowrates (aka: the common process variables) is to force the reaction to proceed in the direction that makes the most desired products. Otherwise stated:

Maximizing the production of desired products depends upon how well Process Operators and Control Board Operators manage the reaction temperatures, reactor pressure, and flowrate of the feedstocks into the reactor inlet.

 

Take Home Messages: Process temperatures can increase due to exothermic chemical reactions. Chemical reactions occur in process industry equipment called reactors. Exothermic reactions are easy to identify because the process stream temperature at the reactor outlet will be greater than the process stream temperature at the reactor inlet.

Written chemical reactions describe  the chemical reactions that go on in process industry reactors.

The reactants of a written chemical reaction are on the left side of the arrow. In the real world of processing, reactants are the feedstocks that flow into the reactor inlet.

The products of a written chemical reaction are on the right side of the arrow. In the real word of processing, the products of the chemical reaction are the components in the reactor effluent that flows out of the reactor outlet.

The intermediate products in a written chemical reaction are the byproducts made in an industrial reactor.

Process Operators and Control Board Operators are responsible for optimally controlling reaction temperature, reactor pressure, and feedstock flowrate to optimize production of the desired reactor product and minimize production of byproducts.

©2015 PTOA Segment 00027
Process Industry Stationary Equipment: Reactors

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