Case Study
Background
A continuous supply of high-purity boiler feedwater is critical for the stable operation of various industries. A multinational chemical company operating a refinery in Texas is an example that uses an Operation and Maintenance (O&M) firm to manage a containerized reverse osmosis (RO) system for boiler feedwater production for the refinery. The RO system consists of three skids in a 10:5:3 pressure vessel array with six elements per vessel. When one set of membranes is taken offline for cleaning, a second set is installed to ensure continuous service. The RO permeate is treated further via ion exchange before entering the boiler feed system.
O&M Strategy
In December 2020, as part of an ongoing focused improvement project, a parallel membrane study was conducted to assess the relative merits of three major RO membrane supplier products in the containerized RO skid. The focused improvement goals are listed in Table 1.
| Table 1: O&M Improvement Project Goals |
| 1. Increase time between membrane cleanings |
| 2. Increase the membrane life cycle: a. Decrease total number of membrane cleanings per membrane (equipment life improvement); b. Reduce membrane early failure rate (damage / performance) |
| 3. Improve water quality: decrease % rejection drop rate between membrane cleanings |
| 4. Reduce labour hours associated with RO membrane changeouts |
Due to the adverse (extremely variable TDS and TSS) nature of the feedwater at this location, a significant portion of the O&M costs is allocated to the frequent cleaning, testing, and RO membrane replacement to meet or exceed water customer quality specifications. As a result, membrane robustness and performance stability were the key membrane properties evaluated, especially after frequent membrane cleanings. LG Water Solutions provided its highest rejection and anti-fouling membrane model, BW 400 R G2, tested against two equivalent competitor models (see Figure 1).
“Throughout the pilot study, LG BW 400 R G2 membranes have maintained their position at the top of
all performance metrics. Combined with outstanding physical design attributes resulting in increased
longevity and reduction in labor hours, LG BW 400 R G2 is our number one choice for replacement
membranes, with hundreds installed within the last six months.”
Robert M, O&M Manager
Membrane Pilot
The test membranes were loaded in three pressure vessels in the first stage of one skid. During cleanings, membranes in Set A are taken offline while Set B is installed to continue operation. When Set B requires cleaning, the newly cleaned Set A membranes are re-installed. The permeate production was set at 26.5 ±0.5 gpm for each pressure vessel at start-up and after each clean-in-place (CIP) cycle by adjusting individual permeate flow control valves. The permeate pressure after each pilot pressure vessel was also recorded. As per the requirements of the RO system, the test elements typically underwent an offsite cleaning every two weeks due to various organics and inorganics that led to a high fouling tendency of the feed water.
The CIP protocol is as follows:
- Cleaning at pH 11.2 followed by pH 2.7 (+/- 0.2)
- Two hours at 95°F at each pH
- High-velocity cleaning using specific RO cleaning chemicals
Results
When compared to other RO membrane models, the membrane study revealed the following about LG
NanoH2O™ RO membranes:
- LG BW 400 R G2 performed with less variation in normalized permeate flow (NPF) rate and its decline
throughout numerous cleaning cycles over more than 15 cleanings in a period of nearly 14-months - After frequent cleanings, BW 400 R G2 in both sets produced the lowest normalized salt passage, while
competitor membranes experienced a considerable increase.
Using highly durable membranes can significantly extend the life cycle of a RO system by reducing membrane
replacements caused by losses in permeability and salt rejection. The membrane study established the value and
durability of LG BW 400 R G2 membranes in an industrial plant setting with high fouling conditions and frequent CIP
requirements that commonly lead to quicker membrane performance loss over time.