Early impressions of Thermo Mercury Freedom System

We are in the early stages of commissioning two new Thermo Fisher Scientific Mercury Freedom Systems at St Johns River Power Park in Jacksonville, FL. It is nice to have a customer who has decided to be an early adopter of this technology. There are still a lot of unanswered questions and uncertainty but I think that it is ultimately wise to jump in and get the system installed, get hands on experience, and develop your in house expertise as early as possible.

The mercury systems were added to an existing project to replace the NOx/SOx CEMS that were installed in 1994. We spent a considerable amount of time specifying the NOx/SOx systems but did not have much time to add the mercury systems to the specifications. After looking at the available options, the plant decided that the best option was to go with Thermo. I got up to speed on the mercury regulations and technologies as quickly as possible and added the equipment to the specification.  

We decided to use the Thermo supplied rack. In hind sight we should have chosen to purchase the components and install them in Hoffman racks to match the other systems. We specified the NOx/SOx dilution air train to be able to supply the 3cfm required for the mercury systems. I decided to let Thermo supply their air cleanup train so that if we had any problems with the system they could not point to the dilution air system as a cause. The plan was to commission the system and then switch to using the common dilution air train and retire the Thermo supplied components. We have hit a snag in that plan. We are going to add a nitrogen generator and use nitrogen as the dilution gas in the mercury system and this requires 6cfm so it looks like the dilution air train supplied with the NOx/SOx will not be able to supply both systems. I am looking for the easiest way to resolve the problem.

 

We were a little disappointed in the layout and design of the cabinet. Some of the dilution air components are installed on the outside of the cabinet. We have removed the beige panels from the front of the rack so that we will not have to unscrew them when we need to get into the cabinet.

The back of the cabinet is pretty cramped. In this picture the umbilical has not been terminated so it is just hanging in the cabinet.

Some of the air cleanup train is mounted to a pull out shelf in the middle of the cabinet.

The vacuum pump appears to be high quality. It probably should have been mounted on a pull out shelf as well to make it easier to get to.

We only have the analyzer and calibrator in the cabinet. The probe controller has been mounted on the stack. All power terminations are made on the stack and the analyzer communicates to the probe controller via a fiber optic line and RS-422 converter. This design variation is known as the 82X probe controller and is recommended for sites that are prone to lightning as this installation in Florida, the lightning capital of the US.

 

We are using the 83i probe for now. We have an agreement with Thermo that will allow us to switch to the GC probe if we desire. The 83i was delivered with the system and a GC was not available prior to commissioning so we went with what we had.

Here is the probe with the stinger and return tube installed. The stinger and “tea cup” at the end are hastelloy. The return tube is Teflon. The support tube is Restek coated stainless. I would have preferred hastelloy and I predict that we will need to replace this item in 2–3 years.

One of the things that we liked about the 83i probe is that it has more room and should be easier to work on than the GC. I’m not entirely sure that this is the case after seeing the GC in person and working on the i. The above picture shows the probe after mounting it to the stack. It looks nice and roomy but notice that the umbilical has not been landed.

With the umbilical landed things start to look more crowded. There is a design tweak that needs to happen here. If you look a the picture below you will see that there is one bulkhead available for three of the lines. Many of the lines however terminate deeper inside the probe and there are a lot of Teflon tubes and fittings in there. You have to be careful routing all of these lines to avoid melting them to the clam shell that heats the probe. This differs from the NOx/SOx probes which typically run stainless lines back to a bulkhead where all of the umbilical terminations are made in one location. This helps to reduce the opportunity for leaks, eliminates the possibility of melting tubing, and makes the probe easier to work on at 2am when you’ve been called out because of a problem.

The 82X probe controller is shown below. As you can see they pretty much took the probe controller guts out of the blue box and mounted them in a NEMA enclosure. This is also a little bit of a rough design. I would recommend specifying a bigger enclosure and scrutinizing the layout a little more. I don’t know if Thermo will be super responsive to your requests so you may have to talk nice to your integrator. We currently have one of these units powered up and have found that the temperature control for the heat trace is a little erratic. We found that there is an upgrade to the responsible component and we should have it on Monday.

We still have a lot of work ahead of us. We will have the base systems installed next week and should be performing daily calibrations. Thermo will be sending us a lamp upgrade for the analyzer as well as a calibration gas hydrator that are now part of the base systems. We have also ordered the mercuric chloride calibrator to perform the weekly system integrity checks and nitrogen generators. These will all need to be installed and tested.

Overall I would say that Thermo has done an excellent job in choosing shier approach to the problem of reliably measuring mercury. The things that I have complained about are minor tweaks and when it comes to the major design decisions that affect the overall performance of the system I don’t think that anyone else can beat them.

I will post more as time allows after we have the systems running. I will also post some details of the system integration with the CEMS PLC and the DAHS.