It is difficult to revamp an existing air-cooled steam surface condenser (ACSSC) for higher throughput, since most ACSSC suppliers have changed to a single-tube row design and have discontinued their multi-tube row design. The challenge is further exacerbated since the ACSSC handles steam under vacuum, and any maldistribution due to the geometric change (from multiple rows to a single row) can severely impact the performance of the revamped ACSSC, thereby negating the purpose of the revamp. The case presented here is for an existing multi-row ACSSC that needs to be revamped for a higher steam throughput by adding additional bays under the constraint of limited space. This article will discuss various available options, from retrofitting the existing ACSSC without increasing the plot space, and augmenting the existing bays with a new set of identical bays, to a combination of both revamp and retrofit. Finally, this work will recommend the option that is most suitable for the specified condition that meets the overall project schedule.
Existing ACSSC. The existing condenser was designed and built during the early 1980s. It was a typical horizontal multi-row design with a slope of 40 mm/m. To cater to a condensing duty of 107 MW, without compromising on the proper distribution of steam across all the bays, two streets of bays (of 10 bays each) were mounted back-to-back on a common manifold (FIG. 1). This design ensured optimum utilization of the plot space.
Process design conditions under the revamp scenario. To increase plant throughput, the capacity of the existing cracked gas compressor was increased, resulting in a corresponding increase in the steam turbine capacity and the condenser capacity by approximately 32%, with steam pressure and ambient conditions remaining the same.
Retrofit vs. revamp: The challenges. Being a brownfield project, the biggest challenge was the availability of plot space for additional bays to cater to the higher heat duty. This challenge was compounded by the following constraints specific to the type of service and technology:
* Ensuring proper distribution of steam at 0.44 bar(a)
* Enabling the exiting supplier, which had already moved into a single-row condenser design, to quote for this previous generation of ACSSC--hence, a study was carried out to evaluate the feasibility of retrofitting the existing condenser bays with larger motors, vis-a-vis revamping the existing 20 bays with additional bays.