# MEMORANDUM

To: Kelly	Fortin,	EPA	Region	4

CC: Eva	Land,	EPA	Region	4	and	Katie	Maness,	Anadarko

From: Sara	Carlson,	Anadarko	and	Rahul	Pendse,	Trinity

Date: July	18,	2014

RE: Revisions	to	the	Proposed	Main Engine	BACT	Limits	in	BlackHawk and	BlackHornet	PSD/Title	V Permit	Application

This	technical	memorandum	discu sses	the	need	for a	different	ap proach	for	establishing best	available	control technology	(BACT)	based	emission limits	and	proposes	revisions to	BACT	limits	included	in	the	BlackHawk	and

the	BlackHornet	drills hip	air	permit	appli cation	submitted	to	E PA	in	September	2013.



### BACKGROUND

The	primary	emissions	source	on drillships	currently	permitted under	OCS	regulations	f or	operation	in	the eastern	Gulf	of	Mexico	(EGOM)	a re	the	diesel‐fi red	drillship	ma in	engines	(main	engines .)		The	prevention	of significant	deterioration	(PSD) permits	issued	for	these	source s	contain	BACT	limits	th at	limit	emissions	for each	pollutant	for	which	PSD	review	was	triggered.		The	BACT	li mits	are	provided	in	th e	form	of	grams	per kilowatt‐hour	(g/kW‐hr)	measured over	an	appropriate	averaging period	for	each	pollutant.

Compliance	with	the	BACT	limits in	g/kW‐hr	may	be	demonstrated via	an	EPA‐approved continuous	emissions monitoring	systems	(CEMS),	EPA‐approved	parametric	monitoring	m ethod,	or	with	prior written	approval	by the	EPA,	an	EPA	approved	source testing	emission s	monitoring	me thod.		The	BlackHawk	and	the	BlackHornet drillships	will	be	equipped	with the	parametric	monitoring	syst em.		However,	in	order	to	establish representative	emission	factors	a nd	the	BACT	limits	for	the	mai n	engines	on	these	drillships,	Anadarko

conducted	the	source	tests	accord ing	to	USEPA	methods	under	an approved	test	protocol. The	source	tests	were completed	in	June	2014 and	the	report	was	su bmitted	to	USEPA	on July	12,	2014.		Consistent	with	the	previous air	permit	application s	submitted	to	EPA, BACT	limits	were	prop osed	in	g/kW‐hr	in	the	a ir	permit	applications for	these	drillships.



### NEED FOR REVISIONS TO BACT LIMITS

USEPA	requires	operators	to	test at	various	operating	loads	for three	1‐hour	source	test	r uns	at	each	load.		The

tested	loads	are	intended	to	be	s elected	to	be	most	representat ive	of	the	expected	range of	operating	conditions. The	expected	operating	loads	for the	BlackHawk	and	the	BlackHor net	drillships	is	expect ed	to	vary	between	30 and	60	percent.		The	distribution	of	operating	loads	in	this	ra nge	is	determined	by	the particular	operations being	performed	by	the	ship	and the	requirements	of	dynamic	pos itioning.

In	general,	the	source	tests	perf ormed	on	the	drillship	main	en gines	have	indicated	actua l	engine	emissions	vary significantly	with	operating	load.		In	general,	the	g/kW‐hr	emi ssion	rates	increase	as	the	load	decreases.		For some	engines	and	pollutants,	the tested	emission s	are	less	than the	g/kW‐hr	limits	at	high	loads,	but	may	exceed the	g/kW‐hr	limits	at	lower	load s.		In	order	to	reconcile	the	p ermit	with	actual	eng ine	performance	and minimize	potential	non‐compliant situations,	permit	modificatio ns	are	often	necessary to	build	in	more flexibility	for	low	load	conditions.Ms.	Fortin	–	Page	2 July	18,	2014

In	the	pre‐application	setting, estimating	actual	engine	emissi ons	performance	across the	range	of	loads	is difficult	due	to	factors	including	but	not	limited	to	the	follo wing:

Each	engine’s	performance	change s	from	the	test	bed	to	actual	o peration;
Source	test	results	have	shown	t hat	each	engine,	even	of	the	sa me	model,	performs	differently; Emission	control	technologies	su ch	as	turbocharger	do	not	funct ion	efficiently	at	low	loads	since	they	are designed	for	efficient	opera tions	at	higher	loads; Operational	history	may	impac t	future	performance;	and Main	engine	operating	loads	are inherently	dynami c	and	may	not be	comparable	to	the	emission	results	in	a

controlled	test‐bed	environment.

As	can	be	seen,	none	of	these	fa ctors	are	related	to	improper	m aintenance	or	operation	o f	the	engines,	but	the factors	nonetheless	may	have	rea l	impacts	on	actual	emissions	p erformance	and	are	inh erent	to	the	intended use	of	the	engines.

USEPA	has	expressed	the	intent	t o	have	BACT	limits	that	allow	f or	emission	and	fuel	efficiency	comparison among	main	engines	on	different	dr illships,	and	th is	intent	has been	the	driving	force	behind	having	the	BACT limits	in	g/kW‐hr	for	each	pollutant	and	each	engine.		Given	th e	discrepancy	between	l ow	load	and	high	load emissions	shown	by	rec ent	emissions	tests	an d	the	magnitude	in the	difference	between	l ow	load	and	high	load emissions	for	some	pollutants,	t he	BACT	limits	given	in	terms	o f	a	single	g/kW‐hr	applicable	to	all	loads	will	be very	challenging,	if	not	impossible,	to	comply	with.		In	Anadar ko’s	and	Trinity’s	opinion,	an	approach	to	help

minimize	the	above	mentioned	issu e	would	be	to	define	the	BACT emission	limits,	as	pr oposed	in	Proposed

BACT	Limits	section	of	this	memo randum,	to	consi der	the	trend	o bserved	in	recent	source	test	results	without significantly	sacrificing	emissi on	and	fuel	efficiency	comparis on	opportunities	provided	by	g/kW‐hr	limits.



### PROPOSED BACT LIMITS

For	some	engines,	source	tests	h ave	shown	that,	although	emissi ons	in	terms	of	g/kW‐hr	a re	higher	at	low	loads,

the	absolute	mass	emi ssion	rates	(lb/hr)	a re	often	lower	at	low loads	when	compared	to	high	loads	indicating that	g/kW‐hr	emission	factors	are	important	for	limiting	emissi ons	for	higher	loads	but become	less	important as	loads	decrease.		Inability	of	emission	control	technologies to	work	efficiently	at	lower	loads	is	the	key contributor	to	higher g/kW‐hr	results	at	lo wer	loads.		Situatio ns	where	lower	load	condi tions	with	low	absolute emission	rates	exceed	the	specifi ed	g/kW‐hr	limit	may	result	in counterintuitive	scena rios	where	increasing

absolute	emissions	could	be	a	co rrective	action	to	eliminate	si tuations	that	could	be	viewed	as	“non‐compliant.” To	minimize	this	potential	and	m inimize	the	need	for	future	per mit	modifications,	a	hybri d	limit	that	considers both	lb/hr	and	g/kW‐hr	emi ssions	may	be	appropriate.

The	proposed	methodology	is	to	h ave	a	g/kW‐hr	limit	for	higher loads	where	the	g/kW‐h r	tend	to	be	more constant	and	have	a	lb/hr	limit for	lower	loads where	the	lb/hr emissions	tend	to	vary	less	than	the	g/kW‐hr emissions.		The	key	to this	approach	is	se lecting	the	load	(ref erred	as	BACT	Limit	Switch	Load	hereinafter) below	which	a	lb/hr	emission	lim it	and	above	which	g/kW‐hr	emis sion	limit	is	used	for	compliance demonstration.		For	main	engines on	the	BlackHawk	and	BlackHorn et	drillships,	50%	load	is	proposed	as	the

BACT	Limit	Switch	Load	since	the emission	control	technologies are	expected	to	operate	e fficiently	at	50%	and higher	loads.		The	proposed	BACT limits	for	main	engines	on	the BlackHawk	and	BlackHornet	drillships	are

listed	in	the	table	below.Ms.	Fortin	–	Page	3 July	18,	2014

Proposed BACT Limits for 9H32 Series Main Engines

Proposed BACT Limits NO x CO VOC PM PM 10 PM 2.5 GHG

50% load and above (g/kW

‐ hr) 10.57	 2.49	 0.92	 0.49	 0.49	 0.49	 837

Below 50% load (lbs/hr) 52.41	 12.35	 4.58	 2.41	 2.41	 2.41	 4,149

Proposed BACT Limits for 18H32 Series Main Engines

Proposed BACT Limits NO x CO VOC PM PM 10 PM 2.5 GHG

50% load and above (g/kW

‐ hr) 10.57	 2.49	 0.92	 0.49	 0.49	 0.49	 837

Below 50% load (lbs/hr) 104.82	 24.70	 9.16	 4.82	 4.82	 4.82	 8,299

Having	the	g/kW‐hr	limit	will	still	allow	for	easy	emission	and fuel	efficiency	compari son	across	different	main engines	and	having	the	lb/hr	lim it	will	eliminat e	the	counterin tuitive	scenarios	descri bed	above	and	reduce	the likelihood	for	permit	modificatio ns	due	to	discrepancies	betwee n	low	load	and	high	load	g/kW‐hr	results.