TECHNOLOGY

— Facilities such as oil refining lines, tank farms, filling stations, truck loading/unloading bays, and unloading terminals frequently require oil-gas recovery and purification units. These typically employ a process combining multi-stage deep cryogenic condensation with adsorption or catalytic combustion to ensure effective oil-gas recovery and compliance with exhaust emission standards.

— For instance, a refining and chemical company selected a TMCVS1800 condensation-plus-adsorption oil-gas recovery unit—with a processing capacity of 1,800 m³/h—to handle emissions from its tank farm, zero-level sump (for raw material unloading), and loading/unloading bays.

— The unit employs a graded cooling process; when the oil-gas temperature drops to between -70°C and -75°C, the mass concentration of non-methane total hydrocarbons (NMTHC) in the exhaust air falls below 70 g/m³. To ensure safety and regulatory compliance, the gas undergoes subsequent adsorption treatment, resulting in final NMTHC emission concentrations that meet the requirements of GB 20950-2007, *Emission Standard of Air Pollutants for Oil Depots*.

Process route of the plant system

1. Hydrocarbon vapors vented from the loading arms and oil tank breathers are collected into a main gas collection header;

2. A pressure sensor on the main header transmits pressure signals back to the control system;

3. The control system adjusts the extraction capacity of the variable-frequency fan/pump via a variable-frequency drive (VFD), dynamically tracking the vapor discharge rate during the loading process;

4. The collected vapors are conveyed to the vapor recovery unit. In the condensation unit, the vast majority of the vapors are converted into liquid oil through a staged condensation process and recovered directly to the storage tank; the remaining low-concentration vapors undergo heat exchange to return to near-ambient temperature before entering the adsorption unit;

5. The low-concentration, near-ambient temperature vapors exiting the heat exchanger enter the adsorption unit—comprising two parallel vessels (Tank A and Tank B)—for treatment; clean gas discharged from the adsorption process meets emission standards, while a saturated adsorption vessel undergoes vacuum desorption, with the parallel vessel simultaneously switching to the adsorption phase;

6. The high-concentration gas resulting from desorption enters an absorption tank for treatment; any small amount of unabsorbed vapor is routed back to the condensation system for the next cycle;

7. Once the absorption tank is full, the recovered oil is automatically transferred to the user's storage tank via an oil pump.   
 

Process Principles of Oil and Gas Recovery Units

— Oil and gas at ambient temperature travel along the main pipeline and are conveyed by a downstream explosion-proof air pump into the condensation unit of the treatment system. The air pump is interlocked with a pressure sensor installed on the main pipeline, allowing for automatic variable-frequency operation based on the volume of product being loaded.

— The oil and gas stream first enters a regenerative heat exchanger to exchange heat with the gas that has already undergone condensation; it then proceeds to the condensation unit for multi-stage processing. It is first cooled to 4°C in a precooler, causing some oil and water to condense out. Next, it enters the first-stage condensation chamber and is cooled to -25°C, separating out more oil. It then enters the second-stage condensation chamber and is cooled to -75°C, further separating out oil. By this point, the majority of hydrocarbon components have condensed into liquid and separated out. The resulting low-temperature, lean gas flows back through the first-stage condensation chamber and the regenerative heat exchanger, warming up to near-ambient temperature; this completes the recovery and utilization of cooling energy within the gas circuit. Additionally, the oil discharge line at each cooling stage is equipped with a recovery unit that utilizes superheated vapor discharged from the refrigeration system's compressor to raise the oil temperature above the freezing point; this resolves oil recovery issues and prevents ice blockages or condensation buildup in the discharge lines. The entire cooling capacity of the system is dedicated to overcoming the latent heat of vaporization (converting the gas to liquid), ensuring no cooling energy is wasted.

— Low-concentration oil and gas that were not condensed enter the adsorption system. This system utilizes two adsorption vessels that alternate between adsorption, desorption, and purging cycles. At atmospheric pressure, Vessel A adsorbs the remaining oil and gas components from the feed stream; once saturated, the system automatically switches to Vessel B for adsorption. Simultaneously, Vessel A undergoes vacuum desorption to regenerate the adsorbent. The desorbed oil and gas enter the system's integrated oil collection tank for absorption, while any unabsorbed gas is routed back for another cycle of condensation treatment. Finally, the tail gas—purified to meet discharge standards—is safely vented through a flame arrester.   
 

Complete process flow of the oil and gas recovery unit

✓ Oil and gas collection system   
✓ Oil and gas transfer system   
✓ Oil and gas condensation, liquefaction, and separation system   
✓ Pressure Swing Adsorption (PSA) and desorption system   
✓ Automatic transfer system for recovered oil products   
✓ Anti-backflow system for oil products   
✓ Oil/gas separation system   
✓ Anti-freezing system for oil lines   
✓ Unit automation and control system   
✓ Safety device for the interface between the plant and the oil facility