Process Flow Split Cooling to Reduce Heat Exchanger Thermal Gradients
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Solution Overview
Problem
Conventional methods for cooling process flows using liquefied nitrogen in cryogenic refrigeration and liquefaction systems face challenges such as excessive temperature gradients in heat exchangers, leading to potential damage and reduced operational safety due to high thermal expansion forces, especially during the initial cooling phase from ambient temperature to 80 K.
Innovation Solution
The process flow is divided into multiple partial flows, with flow rates regulated by valves to ensure that only the first partial flow is cooled in both heat exchangers against the auxiliary flow, and subsequent partial flows are admixed to maintain uniform temperatures at the inlet of the second heat exchanger, minimizing temperature differences and reducing thermal load.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the process flow is cooled exclusively by liquefied nitrogen in the first cooling phase, then the cooling efficiency is high, but the temperature difference between heat exchanger channels exceeds the maximum permissible limit, leading to excessive thermal expansion forces and potential heat exchanger damage
Solution Approach 1:
The process flow is divided into multiple partial flows (first partial flow, second partial flow, and optionally third partial flow). The first partial flow is cooled exclusively by liquefied nitrogen in both heat exchangers, while the second partial flow is mixed with the first partial flow before entering the second heat exchanger. This segmentation allows the system to maintain high cooling efficiency while reducing the temperature difference in the heat exchangers to below the maximum permissible limit, preventing thermal expansion damage.
2Temperature
If the process flow is cooled from ambient temperature to 80 K using liquefied nitrogen, then the pre-cooling effect is achieved, but the thermal expansion forces exceed the strength limits of the heat exchanger
Solution Approach 1:
The process flow is pre-cooled from ambient temperature to 80 K using liquefied nitrogen before entering the main refrigeration cycle. By dividing the process flow into partial flows and controlling their mixing points, the system achieves the necessary pre-cooling effect while ensuring that the temperature difference between heat exchanger channels remains below the maximum permissible limit, thereby protecting the heat exchanger from thermal expansion damage.
3Productivity
If the temperature difference between process flow and auxiliary flow is maximized for efficient heat exchange, then the cooling performance is improved, but the thermal expansion forces damage the heat exchanger
Solution Approach 1:
The system dynamically controls the mixing of partial flows at different stages of the cooling process. During the first cooling phase, the first partial flow is cooled exclusively by liquefied nitrogen to maintain efficient heat exchange. The second partial flow is mixed with the first partial flow before entering the second heat exchanger, dynamically adjusting the temperature difference to remain below the maximum permissible limit, thus preventing thermal expansion damage while maintaining cooling performance.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach reduces the maximum temperature difference across heat exchanger channels below the permissible limit, enhancing operational safety and efficiency while maintaining full operational reliability, allowing for the cooling of high-pressure helium streams without exceeding safe temperature gradients.
Implementation Method 1
heat exchange between the process flow and the auxiliary flow taking place in a first heat exchanger and a second heat exchanger connected downstream of this
Implementation Method 2
The circulated auxiliary stream or liquefied nitrogen is separated into a liquid fraction and a gas fraction after it has been expanded to provide cold
Implementation Method 3
the heat of vaporization of the liquefied nitrogen is approximately the same as the enthalpy difference of the nitrogen through saturated steam at ambient temperature
Implementation Method 4
the circulated auxiliary stream or liquefied nitrogen is separated into a liquid fraction and a gas fraction after it has been expanded to provide cold
Data Source
Figure 1
AI summary
What is described is a method for cooling a process flow against an auxiliary flow, wherein the exchange of heat between the process flow and the auxiliary flow takes place in a first heat exchanger and a second heat exchanger downstream of the first. According to the invention: a) the process flow (1) is split into two or more part flows (2, 2a, 2b); b) the mass flows of the part flows (2, 2a, 2b) can be regulated by means of a respective valve (a, b, c); c) only a first part flow (1) is cooled in the first and second heat exchangers (E1, E2) against the auxiliary flow (9, 11); and d) the or the other part flows (2a, 2b) is/are admixed to the cooled first part flow (3), and the process flow thus formed is again cooled in the second heat exchanger (E2), wherein in the case of splitting into more than two part flows (2a, 2b) the process flow is again cooled in the second heat exchanger (E2) after each admixing of a part flow; e) wherein the mass flows of the part flows (2, 2a, 2b) are regulated such that, at the inlet of the second heat exchanger (E2), the temperatures of the process flows to be cooled in the second heat exchanger (E2) differ by no more than 10 K with respect one another; and f) wherein at least one of the valves (a, b, c) regulating the mass flows of the part flows is fully open.