Hybrid indirect evaporative chilling systems help optimize performance
As natural gas usage continues to grow, due to its clean, cost-competitive and efficient nature, the demand for larger capacity compressors has increased. Many operators use gas turbines to drive their compressors due to their power density, ease of operations and low emissions.
One challenge with modern gas turbines is that they lose significant output and efficiency as air temperatures rise, forcing users to accept lower capacity or add incremental equipment to compensate for this loss. Figure 1 shows the performance of several leading gas turbines used to drive compressors.
For one integrated oil and gas firm, Petróleos Mexicanos S.A. de C.V. (Pemex), the opportunity to gain significant incremental gas flow from its existing facilities was very compelling. Pemex worked with Everest Sciences of Tulsa, Oklahoma to evaluate the potential benefits of providing inlet chilling the existing Solar Taurus 60 gas turbines at its Parédon facility. This evaluation showed a significant value proposition, and Pemex issued an international request for proposals in 2014. Everest Sciences and its local partner Equipos Industriales del Golfo (EIGSA) received the contract to supply three hybrid indirect evaporative chilling systems to Pemex in November of 2014, with operations starting in early 2015.
The hybrid indirect evaporative chilling systems t-solution is highly efficient due to its use of indirect evaporative cooling operating in series with mechanical chilling. For most applications, this solution provides the efficiency of evaporative cooling without using incremental water, while still providing the consistent inlet air temperature of mechanical chilling.
Inlet cooling optimizes gas turbine performance by cooling the gas turbine inlet air and providing more mass flow for combustion and increasing the efficiency of the gas turbine compressor. Increased output from existing equipment optimizes the overall facility, leveraging the existing staff, and reduces the overall operating cost on a US$/hp-hour basis.
For the Pemex Parédon project, the modular equipment was factory packaged and tested and then delivered to the site for installation by EIGSA. The two hybrid indirect evaporative chilling systems were installed in late 2015 and commissioned in early 2016. The ability to gain 15 to 25% incremental power continuously over a 12-month period is a key advantage of modular inlet chilling solutions. Future projects with Pemex are expected to complete quickly now that all parties are familiar with the technology.
A key benefit of hybrid indirect evaporative chilling is the automated and reliable operations of the chilling solution, providing a consistent inlet temperature and system gas flow even as the ambient temperature varies, as shown in Figure 2. Gas flow is a key metric for all gas transportation companies. For the Pemex Parédon plant, this reduction in inlet temperature increased the per unit gas flow from 30.0 MMcfd (8.5 x 105 m3/d) to 33.4 MMcfd (946 m3/d) in the coldest month of the year; in the summer it is expected that the per-unit gas flow will increase by an additional 10%.