Temperature regulation

• A capacity with a range between 5 and 40,000 litres depending on the production demand.
• A corrosion resisting material against used reactive products, and even against newborn molecules from the reactions.
• A pressure program with a range between vacuum and 6 bar, but which may go up to 25, 30 bar or even more in case of hydrogenizing processes.
• A temperature program usually located between –20 and +150°c, sometimes at lower temperatures for cryogenically adapted reactors, sometimes at higher temperatures for the distillation of heavier products.

The reactor is sometimes constructed and installed, in order to produce a specific molecule according to a defined reaction path.

However the reactor is often polyvalent to produce various molecules depending on pathways inside pressure and temperature ranges of the device.

The process molecules are tempered and the temperature is regulated by fluid circulation in the jacket of the reactor.

One used regulation technology is direct injection of a disposable fluid in the jacket and the other one is the so-called “monofluid” loop.

The energy skid is the fine chemistry solution to warm up, cool down or control an exothermic reaction.

Le module d’énergies est également utilisé pour réguler la température d’autres appareils que les réacteurs proprement dit : les séchoirs, filtres sécheurs, ”Nutsche” ,… sont également équipés d’une double enveloppe alimentée avec une boucle de fluide thermique ”monofluide”.

The parameter which must be regulated is the reaction temperature. Even if one puts a probe in the reaction, it must not be forgotten that:

TEMPERATURE IS NOT A MEASURABLE PHYSICAL PROPERTY.

Actually, the temperature of a place is evaluated on a scale: 40°c is indeed warmer than 20°c, but one cannot say that the former is twice warmer than the latter.

The Celsius company prefers the use of the Celsius scale, but on occasion, Kelvin or Fahrenheit scales may be used.

• The thermal fluid works in the whole temperature range in the reactor : it is called “monofluid” because it knows no change between high and low temperature operations.
• The thermal fluid circulates constantly inside the jacket reactor with the help of a regulation pump .
• The thermal fluid receives calories and frigories.
• In some cases the monofluid gets, through exchangers, calories and frigories from steam, water, glycoled water, brine…, even liquid nitrogen. In this case, the energy skid runs in an “close loop” manner.
• Or the monofluid gets calories and frigories by direct injection of warmer or cooler fluid. In that case, the energy skid runs in an “open loop” manner.
• The energy skid can also work in a dual mode in a semi-open loop : this works with heat exchangers for some disposable fluids, in injection mode for some other fluids.

The choice of a thermal fluid to transfer calories or frigories to a process depends on temperature and pressure conditions that affect this fluid.

The best thermal fluid is WATER, since it comes with many advantages: very low cost and excellent thermal performance.

However water also has two drawbacks that may prevent from using it:

• Water may be extremely reactive to reactors in the process, which might create an accident in case of containment rupture.
• The specific weight of solid water is lower than this of liquid water. This very rare property of water (only shared with bismuth) is the origin of much damage.

An interesting compromise is this of a thermal fluid based on water:

• BRINE, calcium chloride solution in water, whom fusion point, at a negative temperature, depends on concentration. The thermal performances of brine are higher than those of water, but corrosion from brine limits its use to low temperatures.
• GLYCOLED WATER, a mix of water and glycol ethylene, may be used at low or high temperatures. The addition of glycol brings the advantages of being able to lower the fusion point of water and to reduce saturated steam pressure at high temperatures.

Organic solvents may also be used, pure or with added water, but only at low temperatures to avoid any flaming hazard:

• Ethanoled water, mix of water and ethanol for cold supply network
• Methanol in pure form, for monofluid loop applications in cryogenic mode between –80 and 50°C.

For very low or very high temperatures, or for a working point oscillating between those extreme temperatures, it is necessary to use specific thermal oil.

The use of those oils should be limited to very necessary cases, since they are very expensive but also very flammable.

In France, the use of a thermal fluid at a temperature higher than its flashpoint is ruled by classified installations rules, note #2951.

• For a reactor capacity range between a few litres and several dozen cubic meters. This made of stainless steel, hastelloy or glass lined steel, with a jacket, agitated in variable speed by one or more impellers.
• For a temperature program which is defined for mixing, dissolving, distillation, crystallisation, drying and condensing operations.
• For an industrial site with a network of cooling and heating distribution system.

• A hydraulic engineering to calculate the monofluid loop’s flow rate at every temperature. The functioning set point of the pump varies with the temperature according to the specific curve: at a high temperature, the fluid’s viscosity is lower, the pressure drop in the loop and the jacket is reduced and the flow rate is higher.
• A thermal engineering including variants such as the fluid’s speed in the jacket and in the heat exchanger, the wall’s thickness, the speed and the power of agitator, the physical characteristics of the solvents, the exothermal character of the reaction, etc.
• The calculation of Reynolds and Nusselt numbers and exchange ratio in the heat exchanger and between the reactor and the jacket.

• The solving of a system of differential equations leads to the simulation of the mass temperatures’ evolution in the reaction environment and inside the jacket.

The energy skid is controlled by an automatic system letting the operators concentrating on the chemical side of the reaction instead of having to worry about the pure technical aspects of it.

The automatic system is either provided by CELSIUS or centralized by the customer with the reactor’s other functions according to CELSIUS functional analysis.

• Mass temperature regulation in cascade mode according to the jacket’s temperature.
• Jacket’s temperature regulation.
• Limitation of the difference between those two temperatures.
• Transmitted power regulation.
• Reactive product flow rate regulation.
• Heating or cooling scale.

For the energy skids that regulate a reaction, crystallisation or drying temperature – in a dryer, dryer-filter or ‘Nutsche’ -, it is very difficult to measure the product temperature. For those devices, the regulation mode is similar to this of a thermal fluid temperature in the jacket, with a fixed set point or according to a scale.

CELSIUS has developed a PLC and automation programs dedicated to the temperature regulation of synthesis reactors.

The advantages of this policy are:

• The programs have been standardized and proven over many test days. Programming errors and time wasted on debugging on site are avoided.
• The automatic regulation is supplemented by a process simulation program based on the thermal balances established during the design of the unit. Thus, before the delivery of the Energy Control Unit, its operation is simulated for several weeks. At any time, the mass and loop temperatures are calculated according to the position of the valves. These tests optimize the proportional and integral parameters of each regulator. The Energy Control Unit is then delivered with a preset automation depending on the reactor and its operating conditions. Commissioning takes place in less than a day.
• The Energy Control Unit is piloted from a touch screen (ATEX or not) on the operator’s workstation. It can also be controlled remotely from a computer by WEB link.
• CELSIUS controls the hardware and software evolutions of its automata during the many years of future exploitation of the Energy Control Units and without license constraints. Upon request, CELSIUS provides after-sales service for the devices via WEB link.