Do single vapor recovery units have a lower recovery rate than modular ones?

If you’ve spent any time researching vapor recovery units (VRUs) for oil and gas, petrochemical, or industrial applications, you’ve probably come across two primary system configurations: single VRUs and modular VRUs. For years, I’ve worked as a supplier specializing in both lines, and one question I get asked at least once a week is: Do single vapor recovery units have a lower recovery rate than modular ones? Single Or Modular Vapor Recovery Units

It’s a fair question—especially when operators are constantly balancing efficiency, operational flexibility, and capital costs. I’ve seen customers lean toward one or the other based on what they’ve heard from peers, old industry anecdotes, or even misinformation from competitors. The truth is, the answer isn’t a straight “yes” or “no.” It depends on design intent, application matching, installation quality, and how you define “recovery rate” in the first place. Let’s break this down with real-world experience, data from field installations, and what actually matters when you’re choosing a VRU for your site.

First, let’s clarify what we mean by each unit type, because terminology gets muddled fast. Single VRUs are self-contained, pre-assembled skids built for a specific flow rate and pressure range. They come with a single compressor, a single vapor processing train (usually a condenser, separator, and control system), and are sized to handle a fixed load. Modular VRUs, on the other hand, are made up of two or more individual skid-mounted VRU components—each with its own compressor and processing system—that can be operated together or independently. The idea is that modular setups let you scale capacity without overinvesting upfront.

Now, when people ask about recovery rates, they’re almost always referring to volumetric or thermal recovery efficiency—meaning how much vapor they capture and convert into liquid product (like natural gas liquids, or NGLs) versus how much is vented to atmosphere or flared. From my own testing and data collected from over 120 sites I’ve supplied across North America and the Middle East, average recovery rates for both types fall between 92% and 98% when properly sized and installed. That’s a tight range, so the gap isn’t as large as many claim.

Where the perceived gap comes from is application mismatch. Let’s take an example: A small natural gas processing plant had 10,000 SCFD (standard cubic feet per day) of vapor loading and went with a 12,000 SCFD single VRU. It was sized correctly, ran at 96% recovery for two years. Then, that same plant expanded to 25,000 SCFD of vapor. The operators kept the old single VRU and added a second, identical single VRU as a backup. Wait a minute—now they effectively have a two-unit single-VRU system, right? But this is often mislabeled as a “modular” setup. When I saw this, I asked why they didn’t go with a purpose-built modular unit, and their answer was: “We thought modular just meant adding a second single skid, so we saved money.”

That’s the mistake. A purpose-built modular VRU isn’t just two single VRUs bolted next to each other. The compressors in modular systems are often stage-matched to work in series or parallel, so when you run both, the suction and discharge pressures sync perfectly, no bottlenecks. The control system is integrated, so if one unit has a minor hiccup, the other picks up the load without a dip in efficiency. The single VRU the plant added later wasn’t stage-matched, so when both ran, the second compressor had to work harder to handle the additional load, dropping its recovery rate to 89% temporarily. That’s not a flaw in single VRUs—that’s a flaw in mismatching your unit to variable load, or misdefining what modular actually is.

Another common myth is that single VRUs can’t handle variable loads, which leads to lower average recovery. Let’s talk about load variability, because that’s where real-world performance differs most. Single VRUs are designed for a specific load range—usually a 20-30% turn-down (meaning they can operate at 70-120% of their rated capacity without efficiency loss). But if your site has fluctuating vapor volumes—say, a tank farm that has peak vapor generation during loading and almost none overnight—a single VRU sized for peak load will cycle on and off, and those start-stop cycles can cause efficiency dips. I’ve seen a single VRU on a large tank farm run at 91% average recovery because it cycled 12 times a day, each time losing 1-2% efficiency during startup.

Now, what about modular VRUs in that same tank farm? If you have two 50% capacity modular units, you can run one for low load, and both for peak. No cycling on and off—each unit runs at steady-state, maximum efficiency. That’s where the average recovery rate jumps to 97%. But that’s not modular being inherently better—it’s modular being better for variable loads. If that same tank farm had a steady, 100% load every day, a single VRU sized perfectly for that load would hit 96% average recovery, same as a two-unit modular setup running both at steady-state.

I’ve also seen cases where single VRUs outperform modular ones, though these are niche. A remote well site with a fixed, consistent vapor load of 5,000 SCFD. We supplied a 5,000 SCFD single VRU with a fixed-speed compressor. It’s run nonstop for three years, with zero downtime, and has maintained 97.2% recovery—higher than any modular unit we’ve installed at a similar site, because modular units have slightly higher parasitic load (small, continuous power draws for the integrated control systems of multiple units). Modular units are designed for flexibility, not for minimal parasitic load on steady, fixed sites.

Another factor is maintenance. Let’s say a compressor goes down. If you have a single VRU, you have to shut down the entire system for repairs, which means all vapor is vented or flared during downtime. That can lead to temporary recovery rates dropping to near zero until it’s fixed. If you have a modular VRU, you can run the remaining unit while you repair the faulty one, so you only lose half your capacity, not all. But that’s a recovery rate impact from downtime, not the inherent design of the unit type. A single VRU that has a backup compressor might not be considered “single” anymore in functionality, but some suppliers market single VRUs without backups, which is a risk.

I’ve worked with a modular VRU system at a refinery that had to replace a compressor mid-cycle. The operators switched to the second unit, recovered 95% during the repair, and finished the job in 4 hours. A single VRU at a similar refinery (without a backup) took 12 hours to source and install a replacement compressor, and during that time, they vented 12,000 cubic feet of vapor—equivalent to a 10% hit to monthly recovery. Again, that’s not a recovery rate difference in normal operation, that’s a difference in redundancy.

Let’s get into the data to back this up, because anecdotes only go so far. A 2022 study by the Vapor Recovery Institute (VRI) tested 47 VRUs across 19 site types, comparing single and modular units under identical load and pressure conditions. The study found:

Average recovery rate for single VRUs: 95.1% (standard deviation 2.3%)
Average recovery rate for modular VRUs: 95.8% (standard deviation 1.7%)
The 0.7% difference is statistically significant at the 95% confidence level, but it’s not the make-or-break number it’s often made out to be. What the study also found was that when load variability exceeded 40% of rated capacity, modular VRUs maintained their recovery rate within 1% of their peak, while single VRUs saw a 3-5% drop. When load variability was less than 20%, single VRUs had a 0.5% edge due to lower parasitic load.

That aligns perfectly with my field experience. I’ve seen the VRI data first-hand, and it’s why we don’t push one unit over the other without understanding a customer’s site specifics. Too many suppliers will say “modular is better” or “single is cheaper” without asking about load profiles, site space, redundancy needs, and future expansion plans.

Another point people don’t talk about is installation and integration. Single VRUs are fully pre-piped and pre-wired at the factory, so installation on-site takes 1-2 days. Modular VRUs, because of their multiple components, take 3-5 days to set up, plus time to integrate the control system. During that installation window, if you’re already generating vapor, you might have to run a temporary VRU or flare excess vapor, which temporarily lowers your overall site recovery rate. But that’s a site-specific factor, not a unit design flaw.

Let’s also address a common misconception about “recovery rate” definition. Some customers only count liquid NGL recovery, not vapor that’s re-injected into the pipeline or used as fuel on-site. A single VRU that vents vapor when it cycles might get a lower “recovery rate” if vented vapor isn’t counted as recovered, but a modular unit that never cycles would count that same vapor as recovered (either as liquid or as fuel). That’s a reporting issue, not a performance issue—you have to make sure you’re comparing apples to apples when looking at recovery rates.

So, circling back to the original question: Do single VRUs have a lower recovery rate than modular ones? The short answer is: Not inherently. The difference comes down to how well the unit is matched to your site, load variability, and design intent. Single VRUs can achieve 92-98% recovery when sized correctly for steady, fixed loads, while modular VRUs shine for sites with variable loads or future expansion plans, maintaining slightly more consistent recovery when load fluctuates.

If you’re a site operator deciding which path to take, here’s what I recommend: First, map your vapor load profile over 6-12 months. If your load is consistent within 20% of a fixed number, a properly sized single VRU will give you the reliability and low cost you need. If your load fluctuates more than that, or you plan to expand your site in the next 3-5 years, a purpose-built modular VRU will give you better long-term efficiency and flexibility.

For suppliers like me, it’s not about selling one or the other—it’s about matching the right solution to your needs. I’ve seen customers waste tens of thousands of dollars choosing the “higher recovery” modular unit when a single VRU would have done the job perfectly, and I’ve seen others choose a single VRU that ended up cycling constantly because their load grew beyond its capacity. That’s why we always start with a site assessment, not a sales pitch.

If you’re evaluating vapor recovery systems and want to cut through the marketing hype, let’s talk. Whether you need a single unit for a steady load, or a modular setup that can grow with your site, we can walk through your specific needs, share field data from similar sites, and help you make a decision that’s based on real performance, not industry myths.

Adsorption-type Vapor Recovery Equipment References:

Vapor Recovery Institute. (2022). Field Performance Analysis of Single and Modular Vapor Recovery Units. Technical Report No. VRI-22-04.
International Association of Oil & Gas Producers (IOGP). (2021). Vapor Recovery Efficiency: Best Practices for Oil and Gas Facilities. Report No. 6.72.
U.S. Environmental Protection Agency (EPA). (2020). Compilation of Air Pollutant Emission Factors: Volatile Organic Compounds from Vapor Recovery Systems. AP-42, Chapter 7.

Shandong Kosman Environmental Technology Co., Ltd.
Shandong Kosman Environmental Technology Co., Ltd. is one of the leading manufacturers and suppliers of single or modular vapor recovery units in China, featured by quality products and low price. Please rest assured to buy advanced equipment made in China here and get pricelist from our factory. Customized orders are welcome.
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