Transocean Offshore Deepwater Drilling, Inc. 

Engineering and Technical Support 

Corporate Engineering 

40 CFR 63 Subpart ZZZZ 

The main engines on our rigs are either 320mm or 280mm bore. The 320mm bore 

engines have two separate strokes. 350 & 400mm stroke’s, dependant on the year of 

delivery; our engines delivered before 2000 tend towards 350 and later engines have a 

longer stroke of 400. The 350 stroke engines have a vol of 28.15 L/cyl and the 400mm 

engines have a vol of 32.17 L/cyl. Given that the limit for category 3 engines is 30 L/cyl, 

then these engines are either over or extremely close to this limit. And engines of that 

size are being regulated separately. See below from the EPA 

MODU’s run their power plant to suit DP requirements which, in reality, means that the 

load on any one engine is never above 50% 

\2\ Marine diesel engines at or above 30 liters per cylinder, 

called Category 3 engines, are typically used for propulsion power 

on ocean-going ships. EPA is addressing Category 3 engines through 

separate actions, including a planned rulemaking for a new tier of 

federal standards (see Advance Notice of Proposed Rulemaking 

published December 7, 2007 at 72 FR 69522) and participation on the 

U.S. delegation to the International Maritime Organization for 

negotiations of new international standards (see www.epa.gov/ 

otaq/oceanvessels.com for information on both of those actions), as 

well as EPA's Clean Ports USA Initiative (see http://www.epa.gov/

cleandiesel/ports/index.htm>). 
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April 11, 2012 

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Category 3 marine diesel engines generate NOX, HC, PM 

and CO emissions that contribute to ozone and CO levels above the 

National Ambient Air Quality Standards (NAAQS) for ozone and CO (i.e., 

they contribute to ozone and CO nonattainment) as well as adverse 

health effects associated with ambient concentrations of PM. As 

described in more detail below and in the Final Regulatory Support 

Document, Category 3 marine diesel engines accounted for about 1.6 

percent of nationwide mobile source NOX emissions in 2000. 

They also accounted for about 2.8 percent of nationwide mobile source 

PM emissions in 2000. These percentages are expected to increase as a 

result of increased trade and decreases in emissions from other nonroad 

sources. The contribution of Category 3 marine diesel engines to 

nationwide mobile source HC and CO levels is small, at 0.1 and 0.02 

percent, respectively, in 2000. 

In writing the ruling, the EPA produced an appendicle TO the proposed Toxics rule on 

inventories. In this, the use of Spark Ignited (SI) engines was discussed and the need for 

catalyst treatment. Stationary spark ignition engines are used when running on natural gas 

or methane as opposed to Compression Ignited (CI) engines that are running on liquid 

fuel; in the case of Transocean, Ultra Low Sulfur Diesel (ULSD). From the tables 

included, the source considered was >750 HP (559 kW), no real data was shown from 

engines of the size used offshore, which range from 3,800 kW to 7,000 kW. 

To try and compare using what actual data we have, we find the following: 

We compared the calculated fuel consumption values for an average load and 

extrapolated over the year and over four engines and found that the calculated annual fuel 

consumption was 7,221 tonnes compared to 2007 figures that give annual consumption of 

7,380 tonnes, 98%. Similarly, we extrapolated the NOX readings and calculate that the 

annual figure would be 372 tonnes. As we don’t have available CO and VOC data, we 

extrapolated using ratio’s to give a figure to work from. The results show that our VOC 

reading is 12.5 Tonnes/year/rig. What this shows is that the VOC’s and CO emissions 

from CI (diesel) engines is significantly lower than similar natural gas SI (generic) 

engines. However, this data’s far from complete, as load, size & fuel consumption are all 

missing. Incidentally, Drilling rigs is mentioned in the EPA study list but has absolutely 

no data or a Source Classification Code (SCC). 

The above shows that the diesel engine in general is a significantly lower emitter of CO 

& VOC’s than natural gas engines. 

Additionally, to be able to react to highly aggressive load demands and to ensure that 

power is always available for thrusters to maintain DP position, the main engines cannot 

operate above 50% load so that, should there be a malfunction and the engine need to 
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April 11, 2012 

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Catalyst removed from DD2 SCR. 

shut down, the remaining engine can accept the inrushing load. Modern marine diesel 

engines, that are now used as MODU main engines are designed to run around 85% load, 

this allows the turbocharger to push in the needed excessive air required to get 

combustion up closer to stoichiometric condition of having an air/fuel mixture of 14.6:1. 

What this means in practice is that when fuel is injected into the cylinder at 30% load, the 

air is at 42.3 Bar but at 100%, (from test bed results), the pressure’s 101.8 Bar. This gives 

the higher load much more “air” to combust with, allowing much better combustion. 

In looking at the EPA’s working document on “proposed toxics rule appendices, it shows 

that there is very little data from compression ignition engines, and the data it does have, 

show’s that the CO and VOC’s are very low as opposed to spark ignition engines (natural 

gas engines). The pertinent data has been extracted and shown in a spreadsheet with the 

calculations showing it in comparison to the data Transocean has gathered so far from it’s 

fleet. 

We believe that the use of a oxidizing 

catalyst is further hampered by the 

low loads that predominate on 

offshore platforms. Wartsila, our 

engine supplier has mentioned that it 

is better to run above 25% load, but 

low load operation is expected to foul 

the catalyst earlier, thus leading to 

manual cleaning. This is a time 

consuming and dangerous proposition 

as the exhaust system is not designed 

for removal of a catalyst. We are of 

the opinion that the catalyst will need 

cleaning regularly, similar to what we 

found with the DD1/2 catalyst in the 

SCR that was fitted. 

In discussing Oxidation catalysts with our engine supplier, they have brought up the 

concern that there is a possibility that the catalyst, as well as reducing the CO, will also 

convert the NO to NO2, thus increasing the environmental damage from that gas. See 

Wartsila letter. 
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April 11, 2012 

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In summary, we believe that large offshore diesels should be exempt from CO regulations 

for the following reasons. 

 CI (Compression Ignition, Diesel) engines are extremely low emitters of CO gas 

by default, and emissions can be further reduced by promoting running at efficient 

load levels; >50%. 

 Unlike CO2 & NOX, CO is not a GHG but a pollutant. However, our DP 

deepwater drillships rarely drill in water depths of less than 900 M (3,000 ft.), and 

never less than 500M. This puts the closest a drillship will be to land at approx 

150 km. (93 miles) during normal operations, see attached maps. 

 On these large engines, the oxidation catalyst is designed to work in conjunction 

with an SCR. 

 Given the low loads that are normal operation in offshore drilling, we believe 

fouling of the catalyst will be an issue, resulting in a requirement to remove and 

manually clean the membrane, this has not been accomplished before with this 

equipment and given the location of the exhaust systems, will introduce a 

significant dropped object hazard. 

 Our Supplier has concerns of unintended consequences of operating an oxidation 

catalyst without additionally using an SCR.