Temperature control for chemical research and production

By: Admin
Oct 03 2017

Temperature control in manufacturing is a quintessential part of proper product formation. If the temperature slips above or below the ideal range needed for a particular stage in a manufacturing process, the results can be harmful. So, it becomes increasingly important that the manufacturer not only determine the proper temperature for each stage, but also monitor the temperature inside the machine and receive appropriate feedback. 

Precise temperature control has a significant influence on performance and quality in chemical process engineering. Temperature control is very important to the application of process safety since it can prevent runaway reactions, fires and explosions, and equipment failure. Process temperature is often monitored by temperature control systems that are in place to achieve and maintain a set point or target temperature. These control systems are made up of several components that send and receive signals that result in adjustment of heat transfer rate through the process. When control systems cannot keep process temperature within safe limits, Safety Instrumented Systems (SIS) can provide a second layer of protection.
Temperature control systems consist of transmitters, controllers, and control elements. Transmitters contain sensing elements that measure the process temperature and send a corresponding signal to the controller. The controller compares the actual temperature to the set point temperature and sends a control signal to the control element. The control element alters heat transfer rates to adjust the process temperature to match the set point temperature.

Chemical production grew in every region of the world. Refinery production is expected to increase by more than 20 percent from 2016 through 2040 — largely due to increasing production volumes of renewables, natural gas and crude oil. With a growth trend expected to continue on an upward trajectory, petrochemical and refinery companies are sure to look for solutions by which to increase operational efficiencies and reduce downtime.
Used after process heating operations, temporary cooling solutions such as cooling towers, chillers and air conditioners provide significant benefits. They allow petrochemical and refining companies to avoid project delays and improve their balance sheet by avoiding high cost capital expenditure (CAPEX) commitments on short- to mid-term duration needs.

When considering a temporary cooling system, it is important that the equipment matches the specific demands of the environment. Each downstream project is unique and has different needs, so there is no such thing as a one-size-fits-all approach. Therefore, it is critical to work with a temperature control provider that understands how to design a system that effectively ties into an existing process.

Temperature control is very important to the application of process safety since it can prevent runaway reactions, fires and explosions, and equipment failure. Process temperature is often monitored by temperature control systems that are in place to achieve and maintain a set point or target temperature. These control systems are made up of several components that send and receive signals that result in adjustment of heat transfer rate through the process. When control systems cannot keep process temperature within safe limits, Safety Instrumented Systems (SIS) can provide a second layer of protection.

Temperature control systems consist of transmitters, controllers, and control elements. Transmitters contain sensing elements that measure the process temperature and send a corresponding signal to the controller. The controller compares the actual temperature to the set point temperature and sends a control signal to the control element. the control element alters heat transfer rates to adjust the process temperature to match the set point temperature.
Petrochemical and refining companies worldwide are benefiting from the cost savings and operational efficiencies that temporary cooling solutions can provide.

Maximizing ammonia summer throughput
The process for producing ammonia requires a hydrogen/nitrogen mass feed-rate ratio of exactly 3:1. If either of these mass flows cannot be maintained at an appropriate flow rate consistent with this ratio, then ammonia production will suffer proportionally. The nitrogen required for the reaction comes from the nitrogen contained in air and enters the reactor via a large compressor.

During the summer, air becomes less dense as the ambient temperature increases. Because a compressor is a volumetric machine, the air-mass flow-rate drops inversely in proportion to the outside temperature. In this case, the air-mass flow-rate decreased during peak summertime temperatures to 43,000 lb/hr, with ammonia production dropping proportionally. This is in contrast to the wintertime, when the producer was able to sustain the maximum air-mass flow-rate of 50,000 lb/hr into the reactor.

One method of increasing air throughput to wintertime flow rates is to increase air density by cooling the air entering the compressor suction. In fact, this producer had already put into place an inlet air-cooling system. However, it proved unreliable and could not consistently increase airflow rates. This situation forced the ammonia producer to begin searching for a solution that would consistently maximize air-mass flow throughout the year.

A specialized group of process engineers evaluated various scenarios for providing the required cooling, and they recommended a staged solution. The ammonia producer’s configuration draws ambient air into a filter housing and then directly into the compressor suction. Therefore, in order to minimize system changes, the third-party engineers designed an intake air-conditioning system that cooled ambient air. The ambient air leaves the filter at 50 to 55°F (10 to 13°C) and enters the compressor suction. Special provisions then were designed into the system to minimize compressor-intake pressure drop.

After implementation, the producer was able to increase ammonia production by 38 metric tons/day due to an increase of air-mass flow of approximately 5,550 to 7,500 lb/hr. This solution consistently maintains an air-mass flow-rate between 48,000 to 50,000 lb/hr — even at peak ambient temperatures of 100 to 105°F (38 to 40°C).

Process Cooling of Diluted Bitumen
A large sustainable-energy company was facing a high temperature challenge at its tank-farm facility, located near its main operations north of Fort McMurray, Alberta, Canada. The tank farm provides cooling and blending of hot bitumen to produce diluted bitumen (also called dilbit) for the company’s downstream customers.

The producer anticipated that the facility was at risk of being unable to adequately cool diluted bitumen below the required temperature needed to avoid flashing of light-end vapours. High dilbit temperatures would require a reduction in flow to the tanks just when the operator required the storage and processing capacity the most. Without a cooling solution, the producer faced potential impacts to its operations, including a reduction in facility throughput.

The energy company called in a third-party provider of temperature control solutions that had experience in cooling heavy hydrocarbons and executing the rapid development of temporary projects. A scope review process kicked off the project. Numerous components of the design and engineering phase were studied to simulate and evaluate potential solutions, and to determine the final process system and utility equipment needs for operation.

Upon completion of the scope review and project definition and engineering stages, the bitumen producer decided to have the project designed and installed to a standard that would permit for potentially long-term use in a plant environment. For example, the glycol loop connections would be hard piped, and a cable tray would be used to run cable between electrical gears. Due to the growing complexities of the project, the bitumen producer contracted a Canadian engineering, procurement and construction (EPC) management firm to undertake the engineering and construction phases.

A specialized team of engineers were tasked with the responsibility for technical support and project-management counsel. Key tasks included oversight of power generation and temperature control equipment delivery to the site, and supervision of work efforts with the EPC to ensure equipment was safely and efficiently installed and commissioned.
The temperature control solution, including 4,000 tons of cooling equipment energized by 6 MW of power, was installed by the project partners. The solution currently remains in operation at the bitumen producer’s facility. It successfully provides cooling of up to 192,000 bbd of dilbit from 134°F to below 100°F (57°C to below 38°C).


Preventing damage to a continuous catalytic reformer
The continuous catalytic reformer (CCR) in a refinery connects naphtha-grade material with hydrogen in a series of reactors that contain platinum catalyst. This reaction increases the octane value of the naphtha feed stream so that it is suitable to be blended into the gasoline pool. One of the side reactions, which reduces yields, is the cracking of feed materials into light hydrocarbon gases. Thus, the purpose of a low pressure separator is to remove as many of these lighter hydrocarbons and hydrogen gas from upgraded naphtha hydrogen gas. However, if there is not enough cooling in the low pressure separator, then heavier hydrocarbons will remain in the re-circulated gas. This can cause process problems downstream of the low pressure separator.

A Midwestern refiner was experiencing condensation of heavier hydrocarbons in certain portions of the recycle-gas circuit. This caused a $50 million loss due to significant production downtime and maintenance costs involved with shutting down the CCR in order to fix the recycle-gas compressor system. This issue was significantly worse during the wintertime when portions of the recycle-gas piping were exposed to colder ambient temperatures, which facilitated condensation.

In order to avoid more damage, the refiner needed a solution that could successfully condense heavier hydrocarbons in the separator rather than the downstream piping.
A temperature control expert proposed a solution whereby they used the existing exchanger. However, instead of using plant cooling water as a cooling medium, a glycol solution would be re-circulated from an air-cooled chiller. The proposed solution reduced the gas inlet temperature from about 250 to 40°F (121 to 4°C) at a design duty of 4.3 MMBTU/hr.


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